Schist

Examples of schist are seen in pillars and spires

NPS Photo

Schists are the other metamorphic rocks found in the Black Canyon. They are at the other end of the heat and pressure scale; the original rocks (protoliths) were not buried as deeply so there was less heat and pressure. Although still considered metamorphic, these schists have been altered less because of the lower pressures and temperatures. The main difference between schist and gneiss is the thickness of their internal layers, known as lamellae (pronounced "la MEL lee"). Gneiss has thick lamellae and schist have very thin, fine layers.

There are two kinds of schists found in the canyon: either a mica-rich schist, that has a lot of biotite and muscovite mica, or a schist rich in hornblende, a type of mineral called amphibole. A zone of schist crosses the canyon between Gunnison Point and Pulpit Rock Overlook. Rare minerals such as garnets, sillimanite, staurolite or andalusite can be common in places.

Location
Some of the best places to see schist are among the spires at Gunnison Point Overlook or Kneeling Camel View. The Great Pillars are among the largest examples of schist in the canyon.

 

Hornblende

Hornblende

Hornblende is a member of the solid solution series for amphiboles. Hornblende is the most common occurring amphibole in the canyon and is black or dark green in color. When it fractures, it tends to break at either 60 or 120 degree angles. It contains significant amounts of potassium and fluorite in its chemical formula, which helps determine the color of the mineral. It sometimes forms large masses known as amphibolite or hornblende schists that are made up of thin, black parallel aligned, needle-like crystals.