metamorphic

Slate

Slate; fine-grained foliated metamorphic rock, commonly derived from shale or mudstone

AI-generated identification · may be incorrect

Typically gray, blue-gray, greenish, or purple with dull to silky luster and excellent slaty cleavage, splitting into thin flat sheets. Hardness is about 3–4 Mohs; composition commonly includes quartz, illite/muscovite, chlorite, and minor hematite or pyrite.

Identified September 18, 2026More metamorphic →

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Physical properties

Formation & geological history

Forms by low-grade regional metamorphism of clay-rich sedimentary rocks, usually during mountain building; many deposits are Paleozoic to Precambrian in age. The image strongly suggests foliated slate, though weathering obscures its exact variety.

Uses & applications

Used for roofing, floor and wall tiles, paving, billiard tables, writing slates, and decorative stone; attractive colored pieces may be collected but are generally low-value.

Geological facts

Its cleavage is produced by aligned microscopic mica and clay minerals, not by original sedimentary layering. Slate commonly grades into phyllite as metamorphic intensity increases.

Field identification & locations

Identify it by persistent planar cleavage, fine grain, and ability to split into thin sheets; it is common in metamorphic belts worldwide, including Wales, Vermont, Spain, Brazil, and China. Field confirmation requires a fresh surface and ideally thin-section or laboratory testing.