mineral
Tumbled dark agate or jasper
Microcrystalline quartz (SiO₂), likely chalcedony/jasper
AI-generated identification · may be incorrectHardness about 6.5–7 Mohs; dark brown to black, opaque, with a smooth waxy-to-subvitreous luster and no visible cleavage. The elongated form appears naturally water-worn or tumbled, with possible iron-oxide staining.
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Physical properties
Hardness about 6.5–7 Mohs; dark brown to black, opaque, with a smooth waxy-to-subvitreous luster and no visible cleavage. The elongated form appears naturally water-worn or tumbled, with possible iron-oxide staining.
Formation & geological history
Forms when silica-rich groundwater fills cavities or fractures in volcanic rock, later hardening into chalcedony or opaque jasper; associated deposits range from Paleozoic to Cenozoic. The specimen’s final shape likely results from tumbling or prolonged abrasion.
Uses & applications
Used as a lapidary stone for cabochons, beads, carvings, and decorative objects; common pieces have modest jewelry and collecting value.
Geological facts
Agate and jasper are varieties of microcrystalline quartz distinguished mainly by translucency and patterning: agate is commonly banded or translucent, whereas jasper is generally opaque and massive.
Field identification & locations
Identify by its very high hardness, glass-scratching ability, waxy luster, dense feel, and lack of cleavage; it commonly occurs in volcanic terrains and alluvial gravels. Exact identification would benefit from translucency, streak, and specific-gravity tests.
