<p>Graphite schist (4.2 centimeters across at its widest)
</p><p>Metamorphic rocks result from intense alteration of any previously existing rocks by heat and/or pressure and/or chemical change.  This can happen as a result of regional metamorphism (large-scale tectonic events, such as continental collision or subduction), burial metamorphism (super-deep burial), contact metamorphism (by the heat &amp; chemicals from nearby magma or lava), hydrothermal metamorphism (by superheated groundwater), shear metamorphism (in or near a fault zone), or shock metamorphism (by an impact event).  Other categories include thermal metamorphism, kinetic metamorphism, and nuclear metamorphism.  Many metamorphic rocks have a foliated texture, but some are crystalline or glassy.
</p><p>Schist is an intermediate- to high-grade, foliated metamorphic rock.  It is highly variable in appearance, depending on the mineral content, which is a function of the precursor rock and specific temperature-pressure conditions.  Garden-variety schists form by metamorphism of phyllites.  Schists typically have medium- to large-sized crystals, unlike the microcrystalline nature of slate &amp; phyllite.
</p><p>Schist's foliated texture (= crystals aligned into bands or stripes or layers) is often only seen when specimens are viewed on edge.
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Graphite schist forms by intermediate- or higher-grade metamorphism of coal.  This results in a foliated rock dominated by the mineral graphite (C - carbon).  Graphite schist has a metallic luster, silvery-gray color, a slick and greasy feel, is very soft (H = 1), and easily marks paper.
<a rel="nofollow" class="external text" href="https://www.flickr.com/people/47445767@N05">James St. John</a>
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<a rel="nofollow" class="external text" href="https://www.flickr.com/photos/jsjgeology/16921730322/">Graphite schist</a>