Schist

Schist is a common metamorphic rock with a well-developed foliation (planar texture) that is due to the presence of aligned platy minerals such as mica and/or talc. The pressure in the metamorphic environment arranges the platy minerals so that the flat planes of the mineral flakes are approximately parallel to one another.

Some nonplaty minerals, such as garnets, may also be present. Schist can form from basalt (igneous rock), shale (sedimentary rock), or slate (another metamorphic rock that forms at lower temperatures and pressures).

Certain varieties of schist are quarried for talc, which is used in ceramic glazes, paint fillers, and roofing materials, as well as carriers for insecticides. Vermiculite (a type of mica) from schist in Llano County can be processed to be used as potting soil.

The schist sample in the Texas Rock Kit was collected from the Llano Uplift and is Precambrian in age.