Gneiss
Gneiss is a metamorphic rock that can be made from both igneous and sedimentary parent materials. It has been metamorphically altered under higher temperatures and pressure than schist.
The Role of Gneiss in the Vineyard
Most gneiss is made of granite, schist, or diorite that was metamorphically changed. These rocks are primarily gray, but with lighter and darker streaks running through them. Some are foliated and some are not. Foliated rocks break along planar cleavages; slate is an example.
Gneiss derived from igneous rocks, or Orthogneiss, include metamorphically altered granite. Feldspar, mica, and quartz veins often form distinctive layers. This mineral content is very similar to granite. Gneiss that is derived from sedimentary rocks is called Paragneiss.
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