sedimentary
Yellow Jasper
Silicon Dioxide (SiO2) - variety of Chalcedony
Hardness: 6.5-7 (Mohs). Color: Opaque mustard yellow to tan. Luster: Vitreous to waxy. Crystal Structure: Trigonal (microcrystalline). Cleavage: None (conchoidal fracture). Specific Gravity: 2.58-2.91.
- Hardness
- 6
- Color
- Opaque mustard yellow to tan
- Luster
- Vitreous to waxy
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Physical properties
Hardness: 6.5-7 (Mohs). Color: Opaque mustard yellow to tan. Luster: Vitreous to waxy. Crystal Structure: Trigonal (microcrystalline). Cleavage: None (conchoidal fracture). Specific Gravity: 2.58-2.91.
Formation & geological history
Formed through the accumulation of silica from volcanic ash or water-borne sediment that infiltrates porous rocks, becoming opaque due to high inclusion of iron oxides (goethite/limonite). Found in various geological ages.
Uses & applications
Used primarily in lapidary arts for jewelry, beads, cabochons, and decorative carvings. Industrial uses include historical abrasive tools due to its hardness.
Geological facts
Yellow Jasper was traditionally used as a 'stone of protection' for travelers. Its distinct opacity is caused by mineral impurities; unlike translucent agate, jasper contains up to 20% foreign material.
Field identification & locations
Identify in the field by its opacity (it will not let light through when held to a torch) and smooth, water-worn texture in riverbeds. Commonly found in South Africa, Madagascar, and the USA (California and Oregon).
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