metamorphic
Fine-grained dark metamorphic rock, likely slate or phyllite
Slate/phyllite, composed mainly of mica-group minerals, quartz, and clay-derived minerals
AI-generated identification · may be incorrectDark gray, fine-grained, and dull to subtly silky; likely Mohs hardness 3–5, with planar foliation or cleavage. The white patches may be quartz, calcite, or surface coating/alteration; crystal grains are mostly microscopic.
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Physical properties
Dark gray, fine-grained, and dull to subtly silky; likely Mohs hardness 3–5, with planar foliation or cleavage. The white patches may be quartz, calcite, or surface coating/alteration; crystal grains are mostly microscopic.
Formation & geological history
Formed when shale or mudstone was subjected to low-grade regional metamorphism, typically during mountain building; age cannot be determined from the photograph. It commonly develops strong cleavage that allows splitting into thin slabs.
Uses & applications
Used for roofing, floor and wall tiles, paving, writing slates, and landscaping; attractive pieces may be collected but generally have low commercial value.
Geological facts
Slate is the lower-grade equivalent of phyllite; phyllite commonly has a more pronounced silky sheen from aligned mica. The specimen’s rounded shape suggests natural abrasion or tumbling.
Field identification & locations
Likely slate if it splits into flat sheets with a dull surface, or phyllite if it shows silky sheen and crinkled foliation. Common in metamorphic belts worldwide, including Wales, Vermont, Spain, and India.
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