Question

Describe slate, phyllite, schist, and gneiss in terms of texture and grain size

Answer 1

Slate is a fine-grained, foliated rock composed mainly of clay minerals or micas. Phyllite is created from slate that is further processed so that the texture is similar to very fine grained smoother white mica. It is composed of quartz, sericite mica, and chlorite. Schist is a medium grade rock with medium to large, flat, sheet-like grains complete with quartz and feldspar. Gneiss is a high grade rock. It is created from of granite, or sedimentary rock. Gneiss is known for its alternating layers composed of different minerals.

Answer 2

Slate, phyllite. schist and gneiss are foliated metamorphic rocks.

Slate: It is a low grade metamorphic rock that is hard, brittle and fine- grained. It has well developed cleavage called as slaty cleavage. It is composed of clay minerals or mica. The color of slate varies from light to dark grey but also found in black, green, red, purple and brown colors. It is smooth to touch.

Phyllite: It is fine grained foliated metamorphic rock. It is granulated between slate and schist i.e the size of grains are larger than slate and smaller than schist. It is rich in mica. here the platy minerals are in parallel alignment. It is similar to slate rock.

Schist: It is a hard metamorphic rock that is coarse grained with mica crystals. It is made up of plate shaped grains that can be easily seen by naked eyes which means that platy minerals are predominant in schist. It varies in color but generally shiny. It is smooth to touch.

Gneiss: It is also a hard metamorphic rock that is medium to coarse grained. The grains can be seen by naked eyes. Irregular bands of dark ferromagnesian minerals are present with poor cleavage. It is light colored rock and rough to touch. It is formed by the metamorphosis of granite rock.