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Phyllite

Pictures of Metamorphic Rock Types

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Phyllite is one step beyond slate in the chain of regional metamorphism. Unlike slate, phyllite has a definite sheen. (more below)
Shiny and leafy
Photo (c) 2009 Andrew Alden, licensed to About.com (fair use policy)
Phyllite is from scientific Latin and means "leaf-stone." It's typically a medium-gray or greenish stone, but here sunlight reflects off its finely wavy face.

Whereas slate has a dull surface because its metamorphic minerals are extremely fine grained, phyllite has a sheen from tiny grains of sericitic mica, graphite, chlorite and similar minerals, because with further heat and pressure, the reflective grains grow more abundant and join each other. And whereas slate usually breaks in very flat sheets, phyllite tends to have a corrugated cleavage.

This rock has nearly all of its original sedimentary structure erased, although some of its clay minerals persist. Further metamorphism converts all of the clays into large grains of mica, along with quartz and feldspar. At that point, phyllite becomes schist.

See the Phyllite Picture Gallery for more about this rock type. And for more photos see the Metamorphic Rocks Gallery.

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