Schist is a medium grade metamorphic rock following shales, slates, and phylittes, in the rock cycle of metamorphism. Schist means “to split” which is a hallmark of this rock. Schist can be formed from the igneous rock basalt (orthoschists); or from shale, a sedimentary rock, or slate, a metamorphic rock (paraschists). This metamorphism is caused by tectonics and mountain building events.
Schist has a strong foliation. This allows it to be easily split into thin flakes or slabs. Schist has a coarse texture. The primary minerals in schist rocks are quartz, mica and amphiboles. Schist rocks have mineral grains that are easily seen by the naked eye. Many schist rocks exhibit mineralogical layering, such as quartz layered between mica layers. The large crystals are often referred to as schistosity. Because the large crystals reflect light, schist rocks often have a high luster, making them shiny. Color is variable in schist rocks because of the altering bands of mica and quartz. Schist rocks are found in shades of gray, yellow, and brown. Greenschist is rich in the green mineral chlorite. Blueschist is rich in blue amphibole. Schist often has garnet inclusions.
Schist occurs in Australia, the Southern Alps, the central Otago area, Himalayas, Scotland, Ireland, Brazil, New England, the Colorado River, and in Manhattan.
Schist rocks are used in building houses and walls because of their strength and durability. In the 1920’s, most of the building foundations in NYC, used schist rocks. Decorative rock walls, called “Yonkers Stone” were built with schist rocks which are no longer available.
There are five bedrock layers in NYC. The ground is more stable where schist is closer to the surface of the earth. The schist bedrock in Manhattan, explains why the taller buildings are densely clustered in the Midtown area. Schist rock forms the backbone of the Henry Hudson Bridge in Manhattan. Large schist rocks are present throughout Grand Central Park. Schist is also used as a decorative stone, for jewelry, and as a mineral source.
Twenty seven road tunnels were studied in Japan. The types of rock surrounding the tunnels included black schist, and green schist.
Using accredited schist stonemasons, schist comes directly from the quarry to build beautiful homes throughout the upper North Island in Otago, New Zealand, since 1997.
On the Clutha River in Australia, gold miners, in the 1860’s, constructed houses of schist, and made pathways of carefully chosen schist pavers. They are still standing along the riverbanks and can be seen from boats on the Clutha River.
In conclusion, schist is an ancient metamorphic rock with strong foliation found in many parts of the world. The foliation allows schist to be split into flakes or slabs easily. This makes schist valuable in construction. NYC’s buildings in Manhattan are built upon schist. Homes in New Zealand are currently being built using schist. Schist is also used in jewelry, decorative stones, and in landscaping.
Read also:Hornfels Metamorphic Rocks
