metamorphic
Tumbled garnet-bearing metamorphic rock (probable garnet schist)
Garnet schist; chiefly quartz, mica, feldspar, and almandine garnet (Fe₃Al₂Si₃O₁₂)
AI-generated identification · may be incorrectDark gray-brown, rounded and weathered, with visible reddish-brown granular patches and strong planar foliation. Likely Mohs hardness 5–7 overall; mica gives a silky to dull luster, while garnet is harder and glassier, with no cleavage.
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Physical properties
Dark gray-brown, rounded and weathered, with visible reddish-brown granular patches and strong planar foliation. Likely Mohs hardness 5–7 overall; mica gives a silky to dull luster, while garnet is harder and glassier, with no cleavage.
Formation & geological history
Formed when a clay- or mica-rich sedimentary protolith was buried, heated, and compressed during regional metamorphism, commonly during mountain building. The image cannot establish a precise geological age; such rocks range from Precambrian to younger orogenic belts.
Uses & applications
Primarily a collector specimen or landscaping stone; fresh garnet crystals may be used as abrasives, and schist can occasionally be used as decorative or building stone.
Geological facts
The elongated streaks and layered appearance are characteristic of metamorphic foliation, produced by aligned mica minerals. The reddish spots may be garnet, but could also be iron-stained quartz or weathered sulfide.
Field identification & locations
Look for glittery aligned mica flakes, wavy layers, and hard rounded garnet grains that resist scratching. Common in metamorphic mountain belts worldwide, including New England, the Appalachians, Scandinavia, and the Alps.
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