Back to the full dot-point answer
EnglandGeologyQuick questions
Rock-forming processes
Quick questions on Metamorphism, grade and facies: contact and regional metamorphism, foliation, index minerals and metamorphic facies - Eduqas A-Level Geology
6short Q&A pairs drawn directly from our worked dot-point answer. For full context and worked exam questions, read the parent dot-point page.
What is foliation?Show answer
Foliation is the parallel alignment of platy or elongate minerals (such as mica), produced by directed pressure, which grows and rotates the minerals at right angles to the maximum stress. It is therefore the signature of regional metamorphism and is absent in contact metamorphism, where the pressure is not directed.
What are index minerals?Show answer
Index minerals are stable only within particular temperature and pressure ranges, so their first appearance marks a grade and lets geologists map metamorphic zones. In a metamorphosed mudstone, in order of increasing grade: chlorite (low), then biotite, then garnet (medium), then kyanite and sillimanite (high). A change from chlorite, through garnet, to sillimanite records grade rising towards the most deeply buried, most strongly deformed core of a mountain belt.
What is metamorphic facies in outline?Show answer
A metamorphic facies is a set of mineral assemblages that form under a particular range of temperature and pressure, regardless of the protolith. Named facies (for example greenschist at low grade and amphibolite at higher grade) correspond to fields on a pressure-temperature diagram, so a rock's mineral assemblage records the conditions it experienced. You only need the idea that facies map conditions, not the full diagram.
What is q1?Show answer
State the three agents of metamorphism. [2 marks]
What is q2?Show answer
Explain why regional metamorphism produces foliated rocks but contact metamorphism does not. [3 marks]
What is q3?Show answer
Name the protolith of marble and of quartzite. [2 marks]
Have a question we have not covered?
This dot-point answer is short enough that we have not extracted many short questions yet. Read the full dot-point answer or ask Mo, our study assistant, in the chat for follow ups.