Question

The sequence of increasing grades of metamorphism of a mudstone (shale, claystone, or siltstone) parent rock (protolith) is: slate (lowest grade), phyllite, schist, gneiss (highest grade).
1. Describe the change in grain size from slate to schist
2. How does the texture of phyllite differ from that of schist?
3. Why do you think that the micas (lat minerals) in these rocks are all parallel, r nearly so, to one another?

Answer 1

Answer:

The slate (lowest grade), phyllite, schist, gneiss (highest grade) rocks.

Explanation:

• The slate is hard and fine-grained rocks and has a salty cleavage that is caused by the growth of minerals due to the metamorphose of the grain ground rocks while schist is medium grade sheet-like grain rock.

• The texture of phyllite is very glittery as its a very fine grain size and the grains are flat. Schist has the greatest grain size. Phyllite has a foliated texture but schists consist of scale.

• Minerals like muscovite and biotite are common rocks forming minerals in micas and are found in the igneous rocks with feldspar and quartz, thus they are parallel and very finely grained flakes in the rock.