mineral
Tumbled dark brown stone, likely jasper or iron-rich chert
Microcrystalline quartz (SiO₂), possibly iron-oxide-bearing jasper/chert
AI-generated identification · may be incorrectOpaque dark brown with mottled lighter patches and a smooth tumbled surface; likely Mohs hardness 6.5–7, vitreous to dull luster, cryptocrystalline structure, and no visible cleavage. Specific gravity is typically about 2.6.
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Physical properties
Opaque dark brown with mottled lighter patches and a smooth tumbled surface; likely Mohs hardness 6.5–7, vitreous to dull luster, cryptocrystalline structure, and no visible cleavage. Specific gravity is typically about 2.6.
Formation & geological history
Formed when silica-rich fluids replaced or cemented sediment, with iron oxides producing the brown coloration; age depends on source, commonly Paleozoic to Mesozoic or older. The rounded shape is human-tumbled rather than natural.
Uses & applications
Used as a lapidary stone for cabochons, beads, carvings, and decorative objects; inexpensive collectible material.
Geological facts
Jasper and chert are varieties of microcrystalline quartz and can be difficult to distinguish visually without testing. Iron staining commonly creates brown, red, yellow, or black patterns.
Field identification & locations
Commonly found in sedimentary settings, gravel deposits, and volcanic terrains worldwide, especially India, Madagascar, Brazil, Australia, and the western United States. A glass-scratch test, if appropriate, should show it can scratch ordinary glass; a streak test is usually white to pale brown.
