Ko'proq

7.2: Metamorfik tog 'jinslarining tasnifi - geologiya fanlari

7.2: Metamorfik tog 'jinslarining tasnifi - geologiya fanlari


Metamorfik jinslarning ikkita asosiy turi mavjud: ular yo'naltirilgan bosim yoki kesish kuchi ta'sirida muhitda hosil bo'lganligi sababli yaproqlangan va yo'naltirilmagan bosimsiz yoki nisbatan sirtga yaqin bo'lgan muhitda hosil bo'lganligi sababli qatlamlanmagan jinslar. juda oz bosim. Kvarsit va marmar kabi metamorfik jinslarning ba'zi yo'naltirilgan bosim mavjud yoki yo'qligidan kelib chiqishi mumkin, odatda yaproqlanishni ko'rsatmaydi, chunki ularning minerallari (mos ravishda kvarts va kalsit) tekislanish tendentsiyasiga ega emas (Qarang: Shakl ( PageIndex {8} )).

Metamorfizm paytida tog 'jinsi yo'naltirilgan bosim ostida siqib chiqarilsa, u deformatsiyalanishi mumkin va bu to'qimalarning o'zgarishiga olib kelishi mumkin, natijada minerallar asosiy stressga perpendikulyar yo'nalishda cho'zilib ketishi mumkin (Shakl ( PageIndex {1} ) ). Bu barglarning shakllanishiga yordam beradi.

Metamorfizm paytida tosh qizdirilsa ham siqilsa va harorat o'zgarishi mavjud minerallardan yangi minerallar paydo bo'lishi uchun etarli bo'lsa, yangi minerallarning siqilish yo'nalishiga perpendikulyar ravishda uzun o'qlari bilan o'sish tendentsiyasi mavjud. Bu ota-jinslar slanets bo'lgan ( PageIndex {2} ) -rasmda, ko'rsatilganidek, ko'rpa-to'shak bilan tasvirlangan. Ham isitgandan, ham siqib chiqarilgandan so'ng, tosh ichida yangi minerallar paydo bo'ldi, odatda bir-biriga parallel bo'lib, asl to'shaklari umuman yo'q qilindi.

( PageIndex {3} ) rasmda ushbu effektning namunasi ko'rsatilgan. Ushbu katta toshda ko'rpa-to'shaklari ko'rinib turibdi, chunki qorong'i va engil chiziqlar o'ng tomonga qarab pastga egilib turadi. Tog 'jinsi, shuningdek, bu ko'rinishda gorizontal (odam o'tirgan yuzaga parallel ravishda) gorizontal ravishda kuchli shilimshiq yaproqlarga ega bo'lib, metamorfizm paytida tosh siqilganligi sababli rivojlangan. Ushbu yaproq tekisligi bo'ylab tosh toshlardan ajralgan va boshqa zaif tomonlar ham shu yo'nalishda mavjudligini ko'rishingiz mumkin.

Siqish va isitishning o'zi (rasmda ko'rsatilgandek ( PageIndex {1} )) yaproqlanishiga hissa qo'shishi mumkin, ammo barglarning ko'pi yangi minerallar hosil bo'lganda va eng katta stress yo'nalishiga perpendikulyar o'sishga majbur bo'lganda rivojlanadi (shakl ( PageIndex {2} )). Agar yangi minerallar slyuda singari plastinka yoki amfibol singari cho'zilgan bo'lsa, bu ta'sir ayniqsa kuchli. Yaproqlarni hosil qilish uchun mineral kristallar katta bo'lishi shart emas. Masalan, slanets, slyuda parchalari bilan ko'rish uchun juda kichikdir.

Katlantirilgan metamorfik jinslarning har xil turlari sinf yoki metamorfizm intensivligi va yaproqlanish turi: shifer, filit, shistva gneys (Shakl ( PageIndex {4} )). Yuqorida ta'kidlab o'tilganidek, shifer slanetsning past darajadagi metamorfizmidan hosil bo'ladi va stressga perpendikulyar o'sgan mikroskopik gil va slyuda kristallariga ega. Slate tekis choyshablarga singib ketishga moyildir. Filit shiferga o'xshaydi, lekin odatda yuqori haroratgacha isitiladi; slyuda kattalashib, sirtda yaltiroq bo'lib ko'rinadi. Slanets odatda tekis bo'lgan joyda, filit to'lqinli qatlamlarda hosil bo'lishi mumkin. Shist hosil bo'lishida harorat etarlicha issiq bo'lib, shunda alohida slyuda kristallari ko'rinadigan darajada katta bo'ladi va boshqa mineral kristallar, masalan, kvarts, dala shpati yoki granat ham ko'rinishi mumkin. Gneysda minerallar har xil rangdagi tasmalarga bo'lingan bo'lishi mumkin. ( PageIndex {4} ) d-rasmda ko'rsatilgan misolda qorong'u bantlar asosan amfibolga, ochiq rangli chiziqlar esa dala shpati va kvartsdir. Ko'pgina gneyslarda slyuda kam yoki umuman yo'q, chunki u slyuda barqaror bo'lganidan yuqori haroratlarda hosil bo'ladi. Odatda faqat mudrok, shist va ayniqsa gneysdan hosil bo'lgan shifer va filitdan farqli o'laroq, turli xil ota jinslardan, shu jumladan loy, qumtosh, konglomerat va vulkanik va intruziv magmatik jinslardan hosil bo'lishi mumkin.

Shist va gneyslarni mavjud bo'lgan muhim minerallar asosida nomlash mumkin. Masalan, bazaltdan olingan shist odatda mineral xloritga boy, shuning uchun biz uni xlorit shist deb ataymiz. Slanetsdan olingan narsa muskovit-biotit shist yoki shunchaki mika shist bo'lishi mumkin, yoki garnetalar mavjud bo'lsa, u mika-garnet shist bo'lishi mumkin. Xuddi shunday, bazalt sifatida paydo bo'lgan va amfibol ustun bo'lgan gneys amfibol gneys yoki aniqrog'i an amfibolit.

Agar tosh katta chuqurlikka ko'milib, erish nuqtasiga yaqin haroratga duch kelsa, u qisman erib ketishi mumkin. Ham metamorfozlangan va ham magmatik materialni o'z ichiga olgan hosil bo'lgan tosh ma'lum migmatit (Shakl ( PageIndex {5} )).

Yuqorida ta'kidlab o'tilganidek, ona jinsi tabiati turli xil metamorfik sharoitlarda undan hosil bo'lishi mumkin bo'lgan metamorfik jinslarning turlarini boshqaradi. Turli xil ota jinslaridan metamorfik darajalarda hosil bo'lishi kutilayotgan jinslarning turlari 7.1-jadvalda keltirilgan. Ba'zi toshlar, masalan, granit, pastki metamorfik darajalarda juda ko'p o'zgarmaydi, chunki ularning minerallari bir necha yuz darajagacha barqarordir.

7.1-jadval. Hududiy metamorfizmning turli darajalarida turli xil ota jinslardan hosil bo'lgan metamorfik jinslarning turlari bo'yicha aniq qo'llanma.
Ota-ona toshiJuda past daraja (150-300 ° C)Past daraja (300-450 ° C)O'rta daraja (450-550 ° C)Yuqori daraja (550 ° C dan yuqori)
Mudrokshiferfilitshistgneys
Granito'zgarish yo'qo'zgarish yo'qdeyarli o'zgarish yo'qgranit gneys
Bazaltxlorit shistxlorit shistamfibolitamfibolit
Qumtosho'zgarish yo'qozgina o'zgarishkvartsitkvartsit
Ohaktoshozgina o'zgarishmarmarmarmarmarmar

Past bosim sharoitida yoki faqat cheklangan bosim ostida hosil bo'lgan metamorfik jinslar qatlamlanmaydi. Ko'pgina hollarda, bu ularning chuqur ko'milmagani va metamorfizm uchun issiqlik qobig'ining yuqori qismiga o'tgan magma tanasidan kelib chiqadi. Bu kontakt metamorfizm. Yaproqlanmagan metamorfik jinslarning ayrim misollari marmar, kvartsitva hornfels.

Marmar metamorfozlangan ohaktoshdir. U hosil bo'lganda, kaltsit kristallari kattalashib boradi va mavjud bo'lgan har qanday cho'kindi to'qimalar va qoldiqlar yo'q qilinadi. Agar asl ohaktosh toza kalsit bo'lsa, u holda marmar oq rangga ega bo'lishi mumkin ( ( PageIndex {6} ) rasmda bo'lgani kabi), ammo agar u loy, silika yoki magniy kabi har xil aralashmalarga ega bo'lsa, marmar Tashqi ko'rinishida "marmar". Mintaqaviy metamorfizm paytida hosil bo'lgan marmar - va aslida marmarning aksariyat qismini o'z ichiga oladi - bu yaproqsimon tuzilishga ega bo'lishi mumkin yoki bo'lmasligi mumkin, ammo marmarda yaproqlarni ko'rish oson emas.

Kvartsit metamorfozlangan qumtoshdir (Shakl ( PageIndex {7} )). Unda kvarts ustunlik qiladi va ko'p hollarda qumtoshning asl kvarts donalari qo'shimcha kremniy bilan payvandlanadi. Aksariyat qumtoshlar tarkibida gil minerallari mavjud, shuningdek, dala shpati yoki tosh parchalari kabi boshqa minerallarni ham o'z ichiga olishi mumkin, shuning uchun kvartsitning aksariyati kvarts bilan ba'zi aralashmalarga ega.

Hatto davomida shakllangan bo'lsa ham mintaqaviy metamorfizm, kvartsit (marmar singari) bargli ko'rinishga moyil emas, chunki kvarts kristallari yo'naltirilgan bosimga to'g'ri kelmaydi. Boshqa tomondan, asl qumtoshda mavjud bo'lgan har qanday loy, metamorfizm paytida mika ichiga aylanishi mumkin va bunday slyuda yo'naltirilgan bosimga to'g'ri keladi. Bunga misol ( PageIndex {8} ) rasmda keltirilgan. Kvarts kristallari bir-biriga mos kelmaydi, ammo slyuda hammasi bir-biriga mos keladi, bu ushbu jinsning mintaqaviy metamorfizmi paytida yo'naltirilgan bosim bo'lganligini ko'rsatadi. Ushbu slyuda juda kichik bo'lgani uchun, bu tosh oddiy ko'z bilan yaproqlangan ko'rinmaydi.

Hornfels odatdagidek loy toshi yoki vulqon jinsi kabi mayda donali jinslarning kontakt metamorfizmi paytida hosil bo'ladigan yana bir yaproqlanmagan metamorfik jins (Shakl ( PageIndex {9} )). Ba'zi hollarda, shoxchalar biotit yoki andalusit kabi minerallarning ko'rinadigan kristallariga ega. Agar shoxfellar vaziyatda yo'naltirilgan bosimsiz hosil bo'lgan bo'lsa, unda bu minerallar tasodifiy yo'naltirilgan bo'lib, bir-biriga to'g'ri kelmagan bo'lar edi, chunki ular xuddi bosim ostida hosil bo'lgandek.

Mashq 7.2 Metamorfik jinslarga nom berish

Tavsif asosida quyidagi metamorfik jinslar uchun oqilona nomlarni keltiring:

  1. Slyuda va andalusitning kichik kristallari ko'rinadigan tosh. Slyuda kristallari bir-biriga doimiy ravishda parallel.
  2. Tashqi ko'rinishi va shishasimon yorqinligi bilan juda qattiq tosh. Yaproq barglari haqida hech qanday dalil yo'q.
  3. To'lqinli choyshablarga bo'linadigan nozik taneli tosh. Choyshabning sirtlari ular uchun yorqinlikka ega.
  4. Amfibolning tekislangan kristallari ustun bo'lgan tosh.

Uchinchi ilovaga qarang 7.2-mashq. Javoblar.

Ommaviy axborot vositalari

  • Shakllar 7.2.1 7.2.2, 7.2.3, 7.2.4abd: © Steven Earle. CC BY.
  • Shakl ( PageIndex {4} ) c: Schist tafsiloti © Maykl C. Rigel. CC BY-SA.
  • Shakl ( PageIndex {5} ): Albertovdagi Geoparkdagi Migmatit © Chmee2. CC BY.
  • Shakl ( PageIndex {6} ) (o'ngda): USGS tomonidan tasmali marmardan chiqib ketish. Jamoat mulki.
  • Shakl ( PageIndex {7} ): © Stiven Erl. CC BY.
  • Shakl ( PageIndex {8} ): © Sandra Jonstoun. CC BY.
  • Shakl ( PageIndex {9} ): Fed tomonidan Hornfels. Jamoat mulki.

Metamorfik jinslar: ma'nosi va tasnifi

Ushbu maqolani o'qigandan so'ng siz quyidagilar haqida ma'lumotga ega bo'lasiz: - 1. Metamorfik jinslarning ma'nosi 2. Metamorfik jinslarning to'qimalari 3. Foliatsiya 4. Xususiyatlari 5. Metamorfik sinf 6. Tog 'jinslarining metamorfik jinslarga aylanishi 7. To'qimalarning tasnifi.

  1. Metamorfik jinslarning ma'nosi
  2. Metamorfik jinslarning to'qimalari
  3. Metamorfik jinslarda barglanish
  4. Metamorfik tog 'jinslarining xususiyatlari
  5. Metamorfik daraja
  6. Tog 'jinslarining metamorfik jinslarga aylanishi
  7. Metamorfik jinslarning to'qimaviy tasnifi

1. Metamorfik tog 'jinslarining ma'nosi :

Metamorfik jinslar magmatik, cho'kindi yoki mavjud bo'lgan boshqa jinslarga katta issiqlik va bosim ta'sirida hosil bo'ladi. Tog 'jinslari tarkibiy qismlari yangi xususiyatlarga ega bo'lgan yangi to'qimalarni hosil qilish uchun qattiq holatdagi qayta kristallanishdan o'tadi.

Shunday qilib, har bir metamorfik jinsda u hosil bo'lgan ota jins mavjud. Tog 'jinslari issiqlik, bosim va kimyoviy eritmalar bilan reaksiyaga kirishishi va shu bilan metamorfik jinslarga aylanish jarayoni metamorfizm deb nomlanadi.

Metamorfik jarayonlar eski toshning fizik-kimyoviy xususiyatini butunlay yangilaydi va o'zgartiradi, shunda yangi hosil bo'lgan metamorfik tosh butunlay boshqacha bo'ladi.

Transformatsiya mineralogiya, to'qima, mato va hatto kimyoviy tarkibdagi o'zgarishlarni o'z ichiga olishi mumkin. Metamorfizm toshlarga issiqlik (dafn yoki magmaning yaqin atrofidagi in'ektsiyalaridan), bosim (dafn) ta'sirida, stress (plastinka to'qnashuvidan) yoki ularning hammasi birikmasidan kelib chiqadi.

Ushbu jarayonlar jinslarning bir turini boshqasiga aylantiradi. Metamorfizm bilan bog'liq bosim juda yuqori. Besh, o'n, hatto o'n besh ming atmosfera bosimi mumkin. Bunday yuqori bosimlar er qa'ri ichida juda chuqurlikda mavjud.

Shuni ham anglash kerakki, tog 'jinslarini metamorfizatsiyalash bilan shug'ullanadigan vaqt geologik vaqtdir & # 8211; yuz minglab va hatto millionlab yillar bo'lishi mumkin. Metamorfik jarayon ko'pincha tog 'jinslari orqali kimyoviy faol suyuqliklarning perkolatsiyasi bilan birga keladi.

Eng muhim suyuqlik suvdir. Metamorfizm haroratidagi suv haddan tashqari qizib ketgan, ya'ni u normal qaynash haroratidan ancha yuqori va bu katta bosim tufayli u hali ham suyuq holatda bo'ladi.

Haddan tashqari qizigan suvning aylanishi ionlarni joydan joyga ko'chirish orqali o'zgarishlarga yordam beradi. Issiqlik, bosim va kimyoviy faol suyuqliklar toshga juda uzoq vaqt olib kelganda, tosh o'zgaradi va o'zgaradi.

2. Metamorfik jinslarning to'qimalari:

Ko'pgina hollarda, metamorfozga uchragan jinslar qizdirilib, siqilib, atrofga suriladi, ya'ni deformatsiyalanadi. Masalan, magmatik magistral pluton atrofdagi toshga kirib kelganda, u toshni isitadi, shuningdek, o'zi uchun joy ajratishi va shu sababli ilgari mavjud bo'lgan toshni chetiga tashlab qo'yishi kerak. Ushbu siqish metamorfik to'qima, tosh tarkibidagi donalarning joylashishi nomi bilan birlashtirilgan xususiyatlarni keltirib chiqaradi.

Minerallarning keng tarqalgan tarkibi o'zlarini barglar yoki varaqlarga ajratishdir. Gneissic foliation deb ataladigan navda granitga xos minerallar qarama-qarshi lentalarda joylashgan.

Ochiq rangli minerallar (kvarts va dala shpati) va quyuq minerallar (asosan qora slyuda va shoxblyon) toshlarga chiziqli ko'rinish berib, alohida guruhlarga bo'linadi. Bu lentali granitga o'xshash gneysga xosdir.

Plitali minerallar, masalan, slyuda ko'p bo'lsa, unda slyuda bilan porlab turadigan ko'plab samolyotlar tufayli tosh platy ko'rinishini oladi. Bunga Schistositga xos bo'lgan Schistosity deyiladi, bu dekorativ maqsadlarda juda ko'p ishlatiladigan porloq metamorfik tosh.

Bir nechta metamorfik to'qimalar shu qadar keng tarqalganki, ular maxsus nomlarga ega. Megaskopik tekshiruv paytida tanib olinadigan to'qimalarni tavsiflash uchun quyidagi atamalardan foydalaniladi.

Dislokatsiya metamorfizmiga javoban singan, parchalangan va / yoki granulyatsiyalangan ko'plab donalarni o'z ichiga oladi, bu erda ustun agent differentsial stress hisoblanadi.

Yo'naltirilgan bosim ta'sirida qayta kristallanishni ko'rsatib beradi.

Odatda yaxshi tikilgan chegaralarga ega bo'lgan, ko'p yoki kamroq teng o'lchovli donalar bilan tavsiflanadi.

Folyatsiyani ko'rsatadigan plastinka yoki mayda mineral donalarning (Masalan: slyuda yoki xlorit) diqqatga sazovor qismini o'z ichiga oladi.

Prismatik mineral donalarning (Ex: amfibol) diqqatga sazovor qismini o'z ichiga oladi, ular afzalroq hizalama, chiziqni namoyish etadi.

Boshqa minerallarning qo'shilishlari bilan ajralib turadigan megakristlarga ega bo'lish (Bu ba'zan elak to'qimasi deb ataladi).

Ko'z shaklidagi (lentikulyar) mega-kristallar.

Metamorfik qayta kristallanish natijasida hosil bo'lgan evhedral donalar.

Har qanday don, kelib chiqishi qanday bo'lishidan qat'i nazar, uning atrofidagi donalardan sezilarli darajada katta.

Metamorfik qayta kristallanish natijasida hosil bo'lgan megakrist.

Metamorfik qayta kristallanish natijasida hosil bo'lgan anhedral donalar.

3. Metamorfik jinslarda barglanish:

Metamorfizmning sabablaridan biri bu bosimdir. Yuqori bosim sharoitida siqib chiqarilganda tosh minerallari o'zgarishga majbur. Metamorfik jinslar 14.5-rasmda ko'rsatilgandek ikki xil bosimga duch kelishi mumkin, ya'ni. bilvosita va to'g'ridan-to'g'ri bosim.

Bilvosita bosim toshlarni har tomondan itaradi, shunda materiallar zarralar yoki kristallar orasidagi bo'shliqlarni olib tashlaydi. To'g'ridan-to'g'ri bosim bo'lsa, itarish kuchlari ikki qarama-qarshi yo'nalishda harakat qiladi, bu minerallarning cho'zilib ketishiga va o'zlarini parallel qatlamlarga joylashishiga olib keladi.

To'g'ridan-to'g'ri bosim ta'sirida minerallar ingichka qatlamlarni hosil qilishga majbur bo'lgan bu to'qima barglar deb ataladi. Siqilgan minerallar uzun chiziqli shakllarga aylanadi. Shuni ta'kidlash mumkinki, barcha metamorfik jinslar qatlamlanmagan.

4. Metamorfik jinslarning xususiyatlari:

Agar tosh metamorfik jinsga aylansa, kamon xarakteristikalarining aksariyati o'zgarishi mumkin. Bunday o'zgarishlar yuz beradiki, yangi hosil bo'lgan metamorfik tosh asl jinsiga o'xshamasligi mumkin.

Metamorfik jinslarning muhim xususiyatlari quyidagilar:

Metamorfizm jarayonida jinsdagi kristallar yoki donalarning kattaligi, shakli va oralig'i o'zgaradi. Toshning donalari issiqlik va bosim ta'sirida erishi va birlashishi va kattaroq kristallar hosil qilib qayta kristallanish jarayoniga o'tishi mumkin.

Toshning asl to'qimasi shu tarzda o'zgaradi. Boshqa holatda, yuqori bosim mo'rt donalarni mayda bo'laklarga bo'linishi va shu bilan toshning tuzilishini o'zgartirishi mumkin yoki issiqlik va bosimning birgalikdagi ta'siri tufayli singan singan tosh qattiq kristalli jinsga aylanishi mumkin.

Katta chuqurlikda ko'milgan magmatik tog 'jinslari cho'kindilaridagi bo'shliqlar yuqori bosim tufayli yopilib qolishi mumkin. Bundan tashqari, donlarga ta'sir etuvchi yuqori bosim donalarni kichikroq hajmda siqib chiqarishi mumkin. Bu harakatlarning barchasi toshning hajmini pasaytiradi va shu bilan toshning zichligini oshiradi.

iii. Foliation va bint:

Yuqori bosim ta'sirida kristallar qatlamlanishiga olib keladi, natijada yaproqlar paydo bo'ladi. Tog'ning minerallari bosim ostida qatlamlarga kelganda, minerallar zichligi har xil bo'lsa, turli rangdagi bantlar hosil bo'lishi mumkin. Ba'zan katta issiqlik tufayli tosh qatlamlari buzilib ketishi mumkin.

iv. Mineral tarkibidagi o'zgarish:

Asl jinslarning minerallari yuqori bosim va issiqlik ta'sirida barqarorlikka ega emas. Yangi minerallar hosil bo'lishiga olib keladigan ionlarning qayta tuzilishi bo'ladi.

v. Metamorfik jinslarni toifalash:

Metamorfik jinslar ko'pincha qatlamli va qatlamsiz jinslarga bo'linadi & tashqi ko'rinishiga qarab mezon. Folyatsiyalangan jinslar tasma yoki qatlamli ko'rinishga ega, chunki tosh tarkibidagi minerallar bir tekisda joylashgan. Ular shist, gneys va shiferni o'z ichiga oladi. Qatlamsiz jinslarga marmar, shoxli toshlar va kvartsit kiradi va bantlanmaydi. Ular teng miqdordagi kristallarga ega bo'lgan bitta ustun mineraldan iborat.

5. Metamorfik daraja:

Metamorfik daraja metamorfizmning intensivligi yoki darajasini anglatadi. Vaqt o'tishi bilan dafn bilan bosim va harorat oshgani sayin metamorfik daraja oshadi. Masalan, vaqt o'tishi bilan tosh yer qa'riga chuqurroq va chuqurroq ko'milgan bo'lsa sodir bo'ladi.

Masalan, ko'lga yoki okeanga yotqizilgan loy qatlamini ko'rib chiqing. Cho'kindining keyingi qatlamlari ostiga ko'milganda, loy zichlanib, oxir-oqibat loy toshiga aylanadi. Agar tosh chuqurroq ko'milib, bosim kuchayib ketsa, u yuqori darajalargacha bosqichma-bosqich metamorfozlanadi. Avval shiferga metamorfozlanadi.

Ushbu jarayon davomida bosim va harorat ko'tarilib, toshni qattiq shilimshiq toshga siqib chiqaradi va loy minerallaridan yo'naltirilgan slyudalarga qayta kristallanish jarayoni boshlanadi, ammo hali yaxshi rivojlanmagan. Keyinchalik shifer shistga aylanadi, unda ko'pgina minerallar to'liq qayta kristallanib, deyarli mukammal parallellikka yo'naltiriladi.

Keyinchalik ko'plab yangi minerallar o'sgan gneysga metamorfozlar. Metamorfik daraja yanada oshgani sayin, tosh eriy boshlaydi. Gneys eriy boshlaganda hosil bo'lgan toshga magmatit deyiladi. Agar erish davom etsa, butun tog 'jinslari eriydi va magma hosil bo'lib, magmatik tosh paydo bo'ladi.

Asl jinslar issiqlik va bosimga duchor bo'lganligi sababli, ular o'zgarishga kirishadilar. O'zgarishlar qay darajada sodir bo'lishi ular ta'sir qiladigan issiqlik va bosim darajalariga yoki metamorfik darajaga bog'liq.

(a) Ona jinslarning xususiyatlarini saqlaydigan past darajadagi metamorfik jinslar.

Bu holda jinslar nisbatan past harorat va bosimga duchor bo'ladi. Agar ular dastlab cho'kindi jinslar bo'lsa, ular hali ham to'shak samolyotlari yoki ularning asl tuzilmalari belgilarini ko'rsatishi mumkin.

b) ota-ona jinslaridan farq qiladigan yuqori darajadagi metamorfik jinslar.

Bu holda tog 'jinslari juda yuqori darajada issiqlik va bosimga duch keladi, shuning uchun metamorfizmdan keyin toshning ichki tuzilishi endi asl jinsiga o'xshamaydi.

Mintaqaviy metamorfizmda katta maydonlardagi qobiq jinslari juda chuqurlikda ko'milib, tuzilishida o'zgarishlarga uchraydi. Keyinchalik chuqurlikda ko'milgan jinslar yuqori bosim va haroratga duchor bo'ladi. Shunday qilib, bu holda biz mintaqa bo'ylab turli xil metamorfik darajadagi jinslarni topamiz.

Metamorfik sinflarni aniqlash:

14.4-rasmda slanetsdan hosil bo'lgan turli xil minerallar, quyi qatlam metamorfizmdan yuqori darajadagi metamorfizmga o'tuvchi cho'kindi jinslar ko'rsatilgan. Issiqlikning bir qancha yuqori darajalarida minerallar erib magmaga aylanib, magmatik toshga aylanishi mumkin.

6. Tog 'jinslarining metamorfik jinslarga aylanishi:

A. Cho'kindi jinslarning o'zgarishi:

(1) Slanets, cho'kindi jins kichik loy zarralaridan iborat. Slanets metamorfozga uchraganda, avval shiferga aylanadi. Slate tekis silliq qatlamlar bo'ylab sinishi mumkin. Yuqori haroratda shifer filitga o'zgaradi. Filit tarkibida yaltiroq mikroskopik slyuda minerallarining qatlamli qatlamlari mavjud. Yuqori harorat va bosimga etarlicha ta'sir qilganda, katta yaproqli minerallar hosil bo'ladi. Ushbu holatda tosh Shist deb nomlanadi.

Juda yuqori haroratlarda (taxminan 650 ° C) minerallar bargli qatlamlarga tekislanishni to'xtatadi va ular bosim natijasida paydo bo'lgan stressni bo'shatishga harakat qiladilar va o'z holatlarini yuqori stress holatidan pastki stress holatiga o'tkazadilar. Buning natijasida tosh gneys hosil bo'ladi. Ushbu toshda o'zgaruvchan va rangli minerallarning bantlari ko'rsatilgan. Yorug'lik va qorong'u minerallarning ajralishi metamorfik differentsiatsiya deb ataladi. Yuqoridagi jarayon har qanday metamorfik jinslardan nafaqat slanetsdan gneys hosil qilishi mumkin.

Agar bosim va harorat gneys hosil bo'lish darajasidan oshib ketsa, unda asta-sekin magma bo'lish uchun gneys eriy boshlaydi. Agar ushbu holatdan tosh paydo bo'lsa, unda jins migmatitdir. Migmatitlar gneyslar bo'lib, ular qisman erib, keyin qotib tosh hosil qiladi. Ushbu holatda qorong'i va bargli qatlamlar hali ham ko'rinadi. Ammo ular tekis qatlamlar o'rniga egri qatlamlar kabi ko'rinadi.

(2) Ohaktosh, cho'kindi jins metamorfizmga turlicha ta'sir qiladi. Ohaktosh yuqori bosim va harorat sharoitida bo'lganida minerallar siqilib, kristall donalari orasidagi barcha ichki bo'shliq siqib chiqariladi. Olingan tosh marmar deb ataladigan qattiq silliq toshdir. Marmar qattiq silliq xususiyatga ega va odatda haykaltaroshlik uchun ishlatiladi.

(3) Qumtosh, metamorfizmga uchragan cho'kindi jins, kvartsit deb nomlangan metamorfik jins hosil qiladi. Marmarda bo'lgani kabi, bu metamorfik jins ham qumtosh juda yuqori bosimga duchor bo'lganda hosil bo'ladi, shuning uchun mineral donalar orasidagi barcha ichki bo'shliq butunlay olib tashlanadi, natijada mineral donalarning bitta doimiy massasi paydo bo'ladi.

B. Magmatik tog 'jinslarining o'zgarishi:

Bazaltlarga yuqori bosim tushganda, ammo nisbatan past haroratlarda uning minerallari konversiyalarga uchraydi va yaproqlanadi. Pastroq bosimlarda minerallar yashil rangga ega bo'ladi. Bu holatda metamorfik jinslar yashil shist deb ataladi.

Bu yashil rangga ega bargli to'qimalarga ega. Kattaroq bosimga duchor bo'lganida, yashil rangli minerallar ko'k rangga o'zgaradi va bu holatda tosh ko'k shist deb ataladi. Ushbu shistlar harorat va bosim oshib borganda, ular gneysga aylanadi. Granit va bunday intruziv jinslar yuqori harorat va bosim ta'sirida gneysga aylanadi.

7. Metamorfik jinslarning tekstural tasnifi:

Metamorfik jinslar mavjud jinslarning har qanday turidan hosil bo'lishi mumkinligi sababli, ularning mineral tarkibi boshqa jinslarning jinslariga qaraganda kengroqdir. Ularni tasniflashning oddiy sxemasi bilan qamrab olish mumkin emas, ammo quyida oddiy teksturali tasnif berilgan.

Shuni ta'kidlash kerakki, metamorfik jinslarning aksariyati anizotrop (turli yo'nalishlarda turli xil xususiyatlarga ega). Masalan, shifer siqilish yo'nalishiga perpendikulyar bo'linmalar bilan siqishda juda kuchli va parchalanishga parallel yo'nalishda siqilganda ancha kuchsizroq.

Boshqa barcha yaproqlangan toshlar xuddi shunday yo'l tutishadi. Shunday qilib, ba'zi testlar uchun qiymatlar diapazoni juda katta bo'lishi mumkin. Metamorfik jinslar uchun ba'zi bir keng tarqalgan muhandislik xususiyatlari quyidagi jadvalda keltirilgan.

Marmar metamorfozlangan karbonat jinsi, odatda ohaktosh kabi hosil bo'ladi. Marmar qit'a-qit'aning to'qnashuv zonalari bo'ylab mintaqaviy metamorflangan joylarda va shuningdek, buklangan tog 'zanjirlarining ildizlarida bo'lishi mumkin. Ular ilgari juda ko'p marjon riflari to'plangan sayoz dengiz tokchalari bo'lgan joylarda ham bo'lishi mumkin.

Sof marmar, asosan oz miqdordagi aralashmalari bo'lgan kalsit oq rangga ega, ammo metamorfoz va kimyoviy ohangdorlik darajasiga qarab, ohaktosh tarkibida har xil rang va kristall o'lchamlari bo'lishi mumkin. Marmar haykaltaroshlik uchun tosh sifatida qadrlanadi, chunki u yumshoq va chiroyli rangga ega.

G'ayrioddiy to'qimalar va ranglar ushbu toshni binolar uchun juda qimmatli qoplama toshga aylantiradi. Hindistondagi go'zal Toj Mahal marmardan yasalgan. Shuni ta'kidlash kerakki, marmar sanoat ifloslanishi va kislota yomg'iridan ta'sirlanadi.

Kvartsit tarkibida 95 foiz kremniy tarkibidagi kvarts qumtoshining metamorfozi natijasida hosil bo'ladi. Biz bilamizki, qumtoshlarning shakli pasttekislik va dengiz cho'kindi muhitidir, bu erda kvartsitlar metamorfik muhitda uchraydi. Kontakt metamorfizm, shuningdek, kvartsit hosil qiladi va shunga muvofiq kvartsitni granit intruziyalari atrofida topish mumkin.

Kvarts eroziyaga juda chidamli va o'simliklarni qo'llab-quvvatlamaydi. Shuning uchun u toshli landshaftlar va qo'pol qirralarni hosil qiladi. Kvartsit oqim kanallarida, yo'l kesmalarida va tog 'yonbag'irlarida ko'rinishi mumkin va oraliq shistlardan ajralib turishi mumkin.

Siqilgan kvartsit qattiqlashganda. Bu juda qattiq va kesishga juda chidamli. Shuning uchun u qurilish toshi sifatida kamdan kam qo'llaniladi. Sof kvartsit oq rangga ega. Temir va marganets kabi oz miqdordagi elementlar toshni yashil yoki kulrang ko'rinishga keltiradi.

Ushbu metamorfik tog 'jinsi metamorfozasi natijasida yuqori darajada siqilgan holda hosil bo'ladi. Uning rangi qora-kulrang. Odatda eski buklangan tog 'zanjirlarining ildizlarida uchraydi. Ushbu qatlamning barcha slyuda minerallari siqilish yo'nalishi bo'yicha to'g'ri burchak ostida mukammal darajada tekislanganligi sababli, choyshablarga bo'linishga imkon beradi. U osonlikcha yorilib ketganligi sababli, uni juda katta hajmdagi choyshablar tayyorlash uchun ajratish mumkin.

Slate ob-havoning ta'siriga juda chidamli va shuning uchun u qo'pol tepaliklarda paydo bo'ladi. U parchalanish tekisliklari bo'ylab mo'rt bo'laklar singari sinadi. Ob-havoning o'ziga xos xususiyati va kislota yomg'iriga qarshi turishi tufayli uni sanoatlashgan mintaqalarda tom yopish materiallari sifatida ishlatish mumkin. Slate, shuningdek, yozuvli slanets va qora taxtalarni tayyorlash uchun ishlatiladi. Undan og'irlik va tekislik zarur bo'lgan bilyard stollari tepalarida foydalanish mumkin.

Ba'zi joylarda rangli shifer jozibali to'qimalarga ega qizil, jigarrang, yashil va sariq ranglarda uchraydi.

Oldingi jadvalda ona jinsi, metamorfik sharoitlari va teksturasini ko'rsatuvchi metamorfik jinslar tasnifining qisqacha mazmuni berilgan.

Gneissgacha bo'lgan metamorfizm slanetsida hosil bo'lgan ketma-ketlik quyida keltirilgan:

Bu minerallar tasodifiy joylashtirilgan mayda donali quyuq toshloq tosh. Bu loy toshi va bazaltdan hosil bo'ladi.

Bu ipakdan yaproqlangan tosh, shiferdan ko'ra qo'polroq.

Bu plyonkali tosh, filitga qaraganda ancha donador va yuqori metamorfik darajaga ega. U shifer yoki bazaltdan hosil bo'ladi.

Bu Shistga qaraganda yuqori metamorfik darajadagi yaproqlangan tosh. U bazaltdan hosil bo'ladi.

Bu yaproqlangan, bog'langan tosh. Bu Schistga qaraganda ancha qo'polroq va eng yuqori metamorfik darajaga ega.


Metamorfik tog 'jinslari issiqlik, bosim va kimyoviy jarayonlar ta'sirida o'zgartirilgan, odatda Yer sathidan pastda ko'milgan. Ushbu o'ta og'ir sharoitlarga ta'sir qilish toshlarning mineralogiyasini, tuzilishini va kimyoviy tarkibini o'zgartirdi.

Metamorfik jinslarning ikki asosiy turi mavjud. Foliated metamorfik jinslar issiqlik va yo'naltirilgan bosim ta'sirida hosil bo'lgan qatlamli yoki bantli ko'rinishga ega. Qatlamli jinslarga quyidagilar kiradi: gneys, filit, shist va shifer

Yaproqlanmagan metamorfik jinslar qatlamli yoki bantli ko'rinishga ega emas. Qatlamsiz jinslarga quyidagilar kiradi: shoxli toshlar, marmar, novakulit, kvartsit va skarn.

Ushbu sahifada metamorfik jinslarning ba'zi keng tarqalgan turlarining fotosuratlari va qisqacha tavsiflari keltirilgan.

Gneys - bu yaproqlangan metamorfik tosh bo'lib, tashqi ko'rinishida lenta hosil bo'lib, u donador mineral donalardan tashkil topgan. Odatda tarkibida kvarts yoki dala shpati minerallari ko'p. Yuqorida ko'rsatilgan namuna bo'ylab ikki dyuym (besh santimetr).

Antrasit ko'mirning eng yuqori darajasidir. U etarli miqdordagi issiqlik va bosim ta'sirida kislorod va vodorodning katta qismini haydab chiqarib, yuqori uglerodli materialni qoldirdi. U yorqin, yaltiroq ko'rinishga ega va yarim konkoidal sinish bilan uziladi. U ko'pincha "tosh ko'mir" deb nomlanadi, ammo bu oddiy odam atamasi va toshning qattiqligi bilan unchalik bog'liq emas. Yuqorida ko'rsatilgan namuna bo'ylab ikki dyuym (besh santimetr).

Hornfels - o'ziga xos tarkibga ega bo'lmagan mayda donali qatlamsiz metamorfik jins. U kontakt metamorfizmi bilan hosil bo'ladi. Hornfels - bu magma kamerasi, sill yoki dike kabi issiqlik manbai yonida "pishirilgan" tosh. Yuqorida ko'rsatilgan namuna bo'ylab ikki dyuym (besh santimetr).

Marmar - bu ohaktosh yoki doloston metamorfizmidan hosil bo'lgan qatlamlanmagan metamorfik jins. U asosan kaltsiy karbonatidan iborat. Yuqorida ko'rsatilgan namuna bo'ylab ikki dyuym (besh santimetr).

Lapis Lazuli, taniqli ko'k marvarid moddasi, aslida metamorfik toshdir. Ko'pchilik buni bilib hayron qolishadi, shuning uchun biz uni ushbu fotosuratlar to'plamiga syurpriz sifatida qo'shdik. Moviy toshlar kamdan-kam uchraydi va biz sizning e'tiboringizni jalb qilganiga ishonamiz. Suratdagi dumaloq buyumlar diametri 9/16 dyuym (14 millimetr) bo'lgan lapis lazuli boncuklaridir. Rasm mualliflik huquqi iStockPhoto / RobertKacpura.

Novakulit - zich, qattiq, mayda donali, kremniyli tosh, konkoidal sinish bilan parchalanadi. U diatom (masalan, kremniy dioksiddan tashkil topgan qattiq qobiqni chiqaradigan bir hujayrali suv o'tlari) kabi organizmlar ko'p bo'lgan dengiz muhitida cho'kindi jinslardan hosil bo'ladi. Yuqorida ko'rsatilgan namuna bo'ylab uch dyuymga teng.

Mariposite - bu ko'p jihatdan ishlatilgan so'z. Bu erda yashil slyuda minerallari yoki yashil rang berish uchun etarli miqdordagi yashil mika mavjud metamorfik jinslar haqida gap ketishi mumkin. Oltin izlovchilar oltinni ushbu yashil toshlar mavjud bo'lgan joylarda topish mumkinligini bilib oldilar. Buning sababi shundaki, maripozit oltinning javharidir.

Kvartsit - bu qumtosh metamorfizmi natijasida hosil bo'lgan qatlamlanmagan metamorfik jins. U asosan kvartsdan iborat. Yuqoridagi namuna bo'ylab ikki dyuym (besh santimetr).

Filit - bu asosan juda mayda donali mlyukadan tashkil topgan yaproqsimon metamorfik tosh. Filitning yuzasi odatda yaltiroq, ba'zan esa ajin bo'ladi. Slanets va shistlar orasidagi daraja oraliqdir. Yuqorida ko'rsatilgan namuna bo'ylab ikki dyuym (besh santimetr).

Skarn - mineral tarkibi emas, balki hosil bo'lishi bilan ajralib turadigan tosh. Ko'pincha magma tanasi yaqinidagi karbonatli jinslar kontakt metamorfizm va metasomatizm bilan o'zgarganda hosil bo'ladi. Various minerals, gems, and even precious metals can sometimes be found in skarn.

Schist is a metamorphic rock with well-developed foliation. It often contains significant amounts of mica which allow the rock to split into thin pieces. It is a rock of intermediate metamorphic grade between phyllite and gneiss. The specimen shown above is a "chlorite schist" because it contains a significant amount of chlorite. It is about two inches (five centimeters) across.

Soapstone is a metamorphic rock that consists primarily of talc with varying amounts of other minerals such as micas, chlorite, amphiboles, pyroxenes, and carbonates. It is a soft, dense, heat-resistant rock that has a high specific heat capacity. These properties make it useful for a wide variety of architectural, practical, and artistic uses.

Slate is a foliated metamorphic rock that is formed through the metamorphism of shale. It is a low-grade metamorphic rock that splits into thin pieces. The specimen shown above is about two inches (five centimeters) across.


Geology of Gems

Eugenii Kievlenko (1923-2000) was a prominent Russian geologist with extensive experience in the exploration, discovery, and evaluation of mineral deposits of all kinds. He discovered dozens of gemstone deposits in various parts of Russia and has been credited with reviving the gemstone-cutting industry of the country.

Geology of Gems is the first comprehensive English language publication to place gem deposits into a concise geological and genetic framework which provides an understanding of existing deposits and the environments of their formation. The book is international in scope and covers most major gem deposits, although there is a strong emphasis on former USSR and Russian Federation deposits.

Eighteen chapters are devoted to specific gems (precious corundum, beryl, etc.). Each chapter contains historical and mineralogical data, with discussions regarding chromophores responsible for various varieties. Major gem deposits and districts are described for each country relative to a geological-genetic classification. The text is liberally illustrated with geological and geographic maps, sections (with scales) and other figures, as well as with numerous excellent color photographs.


Classification of Metamorphic Rocks | Geografiya

Metamorphic rocks are classified on the basis of foliation into the following types: 1. Foliated Metamorphic Rocks 2. Non-Foliated Metamorphic Rocks.

1. Foliated Metamorphic Rocks:

Slates are formed due to dynamic regional meta­morphism of shales and other argillaceous rocks. Slates are characterized by the ‘presence of numerous closely- spaced parallel planes of splitting or cleavage’ but the splitting planes of slates are not parallel to the bedding planes rather they form angle with the bedding planes.

Sometimes the angle between the splitting planes and bedding planes becomes obtuse angle. Such structure of slates is known as slaty cleavage (fig. 8.19) which is formed due to compressive pressure exerted on the rocks. The cleavage is always at right angle to the direction of compression. Slates, if subjected to further intense metamorphism due to immense compression, are changed to phyllites or fine-grained mica-schist.

‘Slates, in fact, may be regarded as a special type of fine-grained schist’ (S. W. Wooldridge and R.S. Morgan), Slates are not as much resistant to erosion as are schists and gneisses. They are of varied colours.

II. Gneiss:

Gneisses are coarse-grained metamorphic rocks which are formed due to metamorphism of conglomer­ates (sedimentary rocks) and coarse gained granites (igneous). Feldspar is the most dominant mineral of gneisses. Like schists, gneisses are also foliated rocks but the foliation is open and is sometimes absent.

There are several types of banded gneisses, which sometimes pass into augen gneiss. The process of granitization or granitification means the transforma­tion of mica-schist to gneiss. Gneissic rocks produce, after weathering and erosion, rounded topography.

iii. Schist:

Schists are fine grained metamorphic rocks and are characterized by well-developed foliation. The word schist has been derived from French word schiste and German word schistose which means to split. When shale sedimentary rocks are subjected to intense compressive force and consequent folding and pres­sure, the clay and other minerals of the original shale rocks are changed to mica minerals due to high pres­sure and temperature and thus shales are changed to schists.

During the process of regional metamorphism the schists get foliated. Schists are named on the basis of dominant minerals e.g., mica-schists, hornblende schists, quartz schists etc.

Mica-schist is the comonest type of schist rocks because it is formed from argillaceous shale sedimentary rock which is a very common rock and is abundantly found on the earth’s surface. Mica- schist is composed of muscovite, biotite, plagioclase and sometimes garnet. Hornblend schists are formed from basaltic rocks and contain hornblende, plagioclase and some quartz minerals.

Green schists are composed of green minerals such as hornblende and chlorites, provided that the rocks are well foliated. If the schists rich in green minerals are poorly foliated, they are called greenstones. The term metabasite is used to name those schists which are formed from basalts or dolerites.

2. Non-Foliated Metamorphic Rocks:

men. Quartzites:

Quartzites are generally formed from sandstones which are dominated by the abundance of quartz min­eral. During the process of metamorphism the voids within the sandstones are compacted due to excessive compression and heat and are also filled with silica, with the result quartzites become very hard and resist­ant to erosion.

When quartzites lie over weaker sedi­mentary rocks like shales or limestones as caprocks, they form stupendous wall-like escarpments. Kaimur escarpment along the left bank of the Son river (in M.P. and Bihar), Bhander escarpments (Satna and Panna districts of M.P.), Rewa escarpments facing the Ganga plains etc. have been formed due to resistant caprocks of quartzitic sandstones resting over shale lithology.

‘The term quartzite is also extended to sandy rocks which have been subjected to cementation by silica deposited from solution. Such rocks are generally softer than the true metamorphic quartzite’s and often behave more like normal sandstones, breaking down into sandy soils’.

Marbles are generally formed due to changes in limestones because of temperature changes. Lime­stones are transformed into marbles due to contact thermal metamorphism during volcanic activity. Lime­stones are also metamorphosed due to dynamic re­gional metamorphism wherein calcium carbonates and other finer particles are changed into calcite.

In fact, the metamorphism of limestones to marble involves a number of changes in the mineralogical characteristics of limestones. For example, the reaction between cal­cium carbonate of limestone during the process of metamorphism produces a new mineral known as wollastonite or calcium silicate.

The colour of marbles depends upon the nature of parent limestones. If the original limestones are devoid of any impurities, the resultant marbles become pure white in colour. The colour changes due to impurities of other materials in the parent limestones.

The marbles of Carrara region of Italy are pure white while the marbles exposed along both the banks of magnificent and stupendous gorge of the Narmada river at Bheraghat near Jabalpur (M.P.) show different grades of colour though white and pink colours dominate.

Dolomites and chalks are also metamorphosed to marbles due to excessive heat but these have only local importance. Marbles are more resistant to erosion than their parent limestones. Besides, they are eco­nomically valuable rocks because they are used as building materials for the construction of very impor­tant buildings as monuments. For example, Tajmahal of Agra and Dilwara temple of Mount Abu (Rajasthan) have been built of marbles.


Characteristics of Metamorphic Rocks

The presence of metamorphic minerals, such as garnet, andalusite, staurolite, sillimanite and kyanite, indicate that the rock has undergone metamorphic processes. These minerals are known as index minerals and can be used to determine a rock’s metamorphic facies.

Exposure to high temperature and pressure conditions cause the reorganizing of crystals within rocks, a process called recrystallization. This will cause an increase in size of individual crystals, which can be observed in the changes of physical properties of, for example, limestone to marble, or a quartzose sandstone to quartzite. The sparry texture and visible crystals present in marble or quartzite visibly differs from the sugary texture of limestone or sandstone, where crystals are not visible or only visible under magnification.


7.2: Classification of Metamorphic Rocks - Geosciences

As with igneous and sedimentary rocks, metamorphic rocks are classified on the basis of texture (grain size, shape, orientation) and mineral composition. However, the classifiction of metamorphic rocks is more difficult to get into than with igneous and sedimentary rocks, for a couple of reasons.
First, is the fact that metamorphism takes place through heat, pressure, and chemically active fluids, but there are many combinations of heat, pressure, and chemically active fluids and so there are many different responses.

Second, any rock - igneous, sedimentary, or metamorphic - can be a parent rock, and so the same heat/pressure/fluid combination can produce markedly different results depending on the type of parent. Or, to put it another way, there is not a direct relationship between the processes of metamorphism and the rocks that result - you have to understand each case on its own.

Third, totally different parent rocks undergoing the same kind of metamorphism can end up looking virtually the same. For example, greenschist (shale parent) and greenstone (mafic igneous parent).

Fourth, the texture terminology we use for metamorphic rocks is used to describe rocks that may have totally different parents, or may be metamorphosed under totally different conditions. The most common example is the term schist.
Schist is a type of layering or foliation found of metamorphic rocks where minerals large enough to be seen by eye tend to line up all in the same direction. But schistose rocks include Greenschist (chlorite dominated), Blueschist (glaucophane dominated, plus many other minerals), and just plain Schist (biotite or muscovite, quartz, and feldspar dominated), and each of these form under different tectonic conditions. To add confusion some rocks with a schist-like texture do not include the term in the name, like amphibolite.
Another example is the texture term gneiss. Gneissic rocks can be produced from both sedimentary and metamorphic parents, and not always under the same metamorphic conditions.

The only way through the problems of metamorphic rock classification is to be very systematic. Once you understand a few basic concepts then we can systematically apply them to clear up some of the confusions. But, you must be clear and systematic
First, we are going to handle each type of metamorphim - hydrothermal, contact, Barrovian, blueschist, eclogite. - separately. The advantage to this is that at the level we do it some types of metamorphism are pretty simple:
Eclogite,. . . produces the rock eclogite.
Contact,. . . produces the rocks hornfels va marble.
Blueschist,. . . produces the rock blueschist.
Hydrothermal,. . . produces rocks such as pegmatite, serpentiniteva soapstone.
Each of these rocks becomes a special case, and all you have to do is memorize them and you have it. Practically what this leave us with is Barrovian metamorphism which is complicated enough we have to deal with it separately.

Second, is to be absolutely clear about metamorphic textures. The same terms are used to describe rocks that come from totally different metamorphic processes, so we must avoid the mistake of assuming that a texture term refers to a particular type of metamorphism. No, a texture term only applies to a description of texture.

Metamorphic Rocks are divided into two basic divisions, summarized in the table below:
1. Foliated/Banded
2. Non-Foliated (also, granular or equidimensional).

The granular rocks are not a big issue. There are a few of them, and we learn each one as a special case. The issue is with foliated textures. The textures themselves are not complicated, there are only three kinds (slaty cleavage, schistosity, and mineral banding) but their relationships to metamorphic processes can be complicated. So, . . . go on to Foliated Texture Discussion


Classifications of Rocks: Sedimentary, Igneous and Metamorphic

Understand the 3 basic rock types and their sub-types with their identification parameters.

Source

What are the 3 basic types of rocks?

Just as any person can be put into one of two main categories of human being, all rocks can be put into one of three fundamentally different types of rocks. They are as follows:

#1. Igneous Rocks

  • Igneous rocks are crystalline solids which form directly from the cooling of magma.
  • This is an exothermic process (it loses heat) and involves a phase change from the liquid to the solid state.
  • The earth is made of igneous rock – at least at the surface where our planet is exposed to the coldness of space.
  • Igneous rocks are given names based upon two things:
    • composition (what they are made of) and
    • texture (how big the crystals are)

    Source

    Source

    The word igneous is derived from the Latin word Ignis which means fire. The rocks formed by the solidification on the cooling of molten magma, are called igneous rocks.

    Depending on where the molten magma cools, they are of the following types:

    Source

    When the molten magma cools deep inside the earth’s crust, intrusive igneous rocks are formed. They:

    • Cool down slowly
    • Form large grains
    • Granite is intrusive igneous rock. Grinding stones used to prepare paste / powder of spices and grains are made of granite.

    Extrusive Igneous Rocks:

    • When the molten magma (lava) comes on the earth’s surface.
    • It rapidly cools down and becomes solid.
    • Rocks formed in such a manner on the crust are called extrusive igneous rocks.
    • They have a very fine grained structure.
    • Basalt is an example of extrusive igneous rocks. The Deccan Plateau is made up of basalt rocks.

    #2. Sedimentary Rocks

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    • These rocks get their name from the Latin word sedimentum which means settle down.
    • These rocks are formed by the settling down of sediments.
    • Sediments are the smaller particles / fragments that are formed by the breaking down of rocks when they roll down, crack and hit each other.
    • These sediments are transported by wind, water etc.
    • These sediments when compressed and hardened form sedimentary rocks.
    • Sandstone is an example of sedimentary rock. It is made up of grains of sand.
    • The sedimentary rocks may also contain fossils of plants, animals and other micro – organisms that once lived on them.

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    #3. Metamorphic Rocks:

    The Greek word ‘metamorphose’ which means change of form, is the root of the word metamorphic. In other words, these are the rocks that are formed when the igneous and sedimentary rocks change their form under the following two circumstances:

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    The following are the examples of metamorphic rocks:

    • Slate: Clay becomes slate after metamorphosis [Texture = Foliated]
    • Marble: Limestone becomes marble after metamorphosis [Texture = Non-Foliated]

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    #4. What is a Rock Cycle?

    The Rock Cycle is a group of changes. Igneous rock can change into sedimentary rock or into metamorphic rock. Sedimentary rock can change into metamorphic rock or into igneous rock. Metamorphic rock can change into igneous or sedimentary rock.

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    NOTE: This lesson forms a part of the series on Physical Geographic Lectures – Click to read the collection