metamorphic
Foliated metamorphic rock (likely phyllite or fine-grained schist)
Phyllite–schist, chiefly quartz, mica, and clay-derived silicates
AI-generated identification · may be incorrectTypically gray-green to silvery gray with silky or satiny sheen, strong foliation, and crinkled/wavy layers; quartz and mica grains are usually microscopic to fine. Hardness is approximately 2–4 for mica-rich surfaces and 6–7 for quartz; cleavage/parting follows foliation, and specific gravity is about 2.7–2.8.
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Physical properties
Typically gray-green to silvery gray with silky or satiny sheen, strong foliation, and crinkled/wavy layers; quartz and mica grains are usually microscopic to fine. Hardness is approximately 2–4 for mica-rich surfaces and 6–7 for quartz; cleavage/parting follows foliation, and specific gravity is about 2.7–2.8.
Formation & geological history
Formed when shale or mudstone underwent low- to medium-grade regional metamorphism, recrystallizing clay minerals into aligned mica and chlorite. Such rocks may range from Precambrian to recent mountain-belt ages, depending on locality.
Uses & applications
Used locally as dimension stone, roofing or paving material, aggregate, and occasionally decorative stone; attractive specimens are collected but are generally low value.
Geological facts
The silky texture and folded foliation reflect pressure-driven mineral alignment during mountain building. It can resemble slate, but phyllite typically has a more pronounced sheen and wavier fabric.
Field identification & locations
Look for continuous foliation, fine grain size, mica sheen, and splitting into irregular sheets; a hand lens may reveal tiny mica flakes. Common in regional metamorphic belts worldwide, including the Appalachians, Alps, and Himalaya.
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