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 Metamorphic Rocks - Slate, Schist and Gneiss.

What is Low and High Grade Metamorphism?

Where do Slate and Schist Come From?

Both slate and schist (pronounced "shist")
are formed from the sedimentary rocks mudstone and shale.
Mudstone and shale are formed from compacted mud or clay.
They are made of very small flat particles like tiny plates,
which have often
become layered during the sedimentary rock formation.

How is Slate Formed?

With additional heat and pressure, the rock particles line up
in the same direction (called "aligning") and form the rock
called slate. This is an example of low grade metamorphism.
The layered structure (called "laminated") allows slate to be
easily split into thin sheets. You have
probably seen dark gray slate sheets used as roofing.

How is Schist Formed?

When mudstone or shale become intensely hot under pressure,
they may form a new metamorphic rock called schist.
Schist can be recognized from its thin layers of interlocking crystals.
It is harder than slate, and may also be split into thin sheets.

How is Gneiss Formed?

The most common metamorphic rock is gneiss
(pronounced "nice").
Gneiss can be formed from a variety of rocks at very high
and pressures.
It is an example of high grade metamorphism and represents
the last stage of changing crystal structure before melting.
Gneiss is usually named after the rock it came from and
often shows alternating layered bands of different minerals.

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