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Minerals and rocks
Quick questions on Metamorphic rocks and processes: contact and regional metamorphism, foliation and recrystallisation - Eduqas GCSE Geology
7short 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 contact metamorphism?Show answer
Contact metamorphism is caused by heat alone from a nearby igneous intrusion. The country rock is "baked" in a zone around the intrusion called the metamorphic aureole, which is widest next to the hottest, largest intrusions. Because there is little or no directed pressure, the minerals recrystallise into an interlocking mosaic with no preferred alignment, giving non-foliated (massive) rocks:
What is regional metamorphism?Show answer
Regional metamorphism acts over a wide area and involves both high heat and high directed pressure, typically where plates collide and mountain belts form. The directed pressure aligns platy minerals, producing foliated rocks (rocks with a layered or banded, easily split fabric). As the intensity (the metamorphic grade) increases, a mudstone passes through:
What is foliation?Show answer
Foliation is the parallel alignment of platy minerals (such as mica) produced by directed pressure. The minerals grow with their flat faces perpendicular to the direction of greatest pressure, creating planes of weakness along which the rock splits. Non-foliated rocks (marble, metaquartzite) lack foliation because they formed under heat without strong directed pressure, or from minerals (calcite, quartz) that are not platy.
What is protolith plus conditions sets the product?Show answer
The metamorphic rock you get depends on what you start with and the conditions:
What is q1?Show answer
State what happens to the minerals in a rock during metamorphism, and what must not happen. [2 marks]
What is q2?Show answer
Name the metamorphic rocks produced from (a) limestone and (b) mudstone under regional metamorphism. [2 marks]
What is q3?Show answer
Explain why marble is not foliated even though it is a metamorphic rock. [2 marks]
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