Schists are a group of metamorphic rocks which are medium to coarse-grained and of a fissile nature, meaning that at least one of the minerals in the rock crystallizes in platy form. Because of this, schists will split easily along these parallel layers. In fact, the word schist comes from a Greek word meaning “to split”.
• How Schists are formed
Schists are formed by regional metamorphism and are associated with tectonics and major mountain building events. Schists are found in regions composed mainly of metamorphic rocks, such as the Central Alps, the Himalayas, Scandinavia, the Highlands of Scotland and north-west of Ireland. They are produced by intense heat, pressure and folding. Schists may be formed from both igneous and sedimentary rocks. Often they are a metamorphosed form of shale. When shale goes through Barrovian metamorphism, it becomes slate first and with greater temperature and pressure will further morph into phyllite and then schist. The depth of burial and the amount of heat and pressure determines the degree of metamorphic changes the shale goes through.
Learn more on how does the phyllite rock form
• Composition
Schists are classified according to the types of rocks they are derived from. There are two major groups: paraschists, which are derived from sedimentary rock like shale; and orthoschists, which are metamorphosed from igneous rock such as basalt. Schists are commonly referred to based on their preponderant mineral composition, e.g. a mica schist would be a schist that consisted mostly of mica. Schists are often a mix of quartz, feldspar, mica, and sometimes amphibole. They may also contain chlorite, garnet or kyanite.
• Color
The color of schist depends greatly on its predominant minerals. Generally, schists may be gray, yellow, green, brown, white, or black.
• Uses for Schists
Schist, with their layers of intermixed minerals, such as quartz, garnet and mica can be very attractive rocks with impressive amounts of shine. Muscovite (mica schist), for instance, is pearlized, reflective and somewhat transparent. Schists are often used in jewelry and other types of artwork. Most schists are rarely used in buildings as the mica can split easily and they are not very strong. However, some types of schists are used in construction. There are buildings at Princeton University and the University of Pennsylvania that were constructed using schist. Schists are often used as decorative stones and in veneers.
