metamorphic

Red jasper cobble

Jasper, an opaque microcrystalline quartz variety (SiO₂), colored chiefly by iron oxides

AI-generated identification · may be incorrect

Typically hardness 6.5–7 Mohs, dense, opaque red to brick-red with black or gray vein-like inclusions, and a dull to glassy luster when polished. It has cryptocrystalline quartz structure, no cleavage, and conchoidal fracture; the rounded form indicates natural or tumbled wear.

Identified September 11, 2026More metamorphic →

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Physical properties

Formation & geological history

Forms when silica-rich fluids replace or cement fine-grained sediment, often incorporating hematite or magnetite; some varieties develop through volcanic silicification. Its exact age cannot be determined visually and may range from Precambrian to recent deposits.

Uses & applications

Used for beads, carvings, cabochons, ornaments, and lapidary work; crushed jasper is occasionally used as decorative aggregate. It has little industrial value compared with ordinary quartz.

Geological facts

The black bands may be manganese- or iron-rich mineral staining, quartz veins, or matrix; the pattern is not diagnostic of a single named jasper variety.

Field identification & locations

Identify it by its opaque red color, very fine grain, lack of cleavage, heavy feel, and inability to scratch with a steel knife; it should scratch glass if fresh and hard. Common sources include India, Madagascar, Brazil, Australia, South Africa, and the western United States.