igneous
Red jasper or glassy volcanic rock (uncertain)
Likely hematite-rich jasper/chert; possibly obsidian with iron-oxide staining
AI-generated identification · may be incorrectSmall polished or naturally glassy, angular specimen with dark red-brown and black areas, vitreous to submetallic luster, and conchoidal-looking fractures. If jasper, hardness is about 6.5–7 Mohs; if obsidian, about 5–5.5; no visible cleavage.
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Physical properties
Small polished or naturally glassy, angular specimen with dark red-brown and black areas, vitreous to submetallic luster, and conchoidal-looking fractures. If jasper, hardness is about 6.5–7 Mohs; if obsidian, about 5–5.5; no visible cleavage.
Formation & geological history
Jasper forms when silica-rich fluids replace or cement sediment, commonly with iron oxides; obsidian forms by rapid cooling of rhyolitic lava. Exact age and locality cannot be determined from the photograph.
Uses & applications
Jasper is used for cabochons, carvings, beads, and ornamental objects; obsidian is used for jewelry, blades, and collectibles. Value is generally modest unless unusually patterned or from a documented locality.
Geological facts
The strong red color commonly comes from hematite or other iron oxides. A steel scratch test, streak test, and close inspection of fracture surfaces would distinguish jasper from obsidian.
Field identification & locations
Common jasper occurs worldwide, especially in volcanic and hydrothermal regions; obsidian is found near young rhyolitic volcanic fields. Test whether it scratches glass and whether its streak is white, red-brown, or absent; avoid testing valuable polished surfaces.
