What does schistose foliation mean?

Question

What does schistose foliation mean?

Answer 1

Metamorphic rocks are rocks that have undergone a change from their original form due to changes in temperature, pressure or chemical alteration. The classification of metamorphic rocks is based on the minerals that are present and the temperature and pressure at which these minerals form. Determination of this information is not easily accomplished in this lab. Therefore, a simplified system is used based on texture and composition.

Texture

Texture is divided into two groups. Foliated textures show a distinct planar character. This means that the minerals in the rock are all aligned with each other. This planar character can be flat like a piece of slate or folded. Non-foliated textures have minerals that are not aligned. Essentially, the minerals are randomly oriented.

Foliation

Foliated textures show four types of foliation. Slaty cleavage is composed of platy minerals that are too small to see. Typically, these rocks split along parallel, planar surfaces. Phyllitic foliation is composed of platy minerals that are slightly larger than those found in slaty cleavage, but generally are still too small to see with the unaided eye. The larger size gives the foliation a slighly shiny appearance. Schistose foliation is composed of larger minerals which are visible to the unaided eye. Platy minerals tend to dominate. Gneissic banding is the easiest of the foliations to recognize. It is composed of alternating bands of dark and light minerals.