sedimentary
Jasper
Jasper (Silicon Dioxide, SiO2 plus iron oxide impurities)
Hardness: 6.5–7 (Mohs scale); Color: Yellowish-brown, mustard, or rust-colored; Luster: Dull or waxy when dry, vitreous when wet or polished; Crystal structure: Trigonal/Microcrystalline; Cleavage: None/Conchoidal fracture; Specific gravity: 2.58–2.91.
- Hardness
- 6
- Color
- Yellowish-brown, mustard, or rust-colored
- Luster
- Dull or waxy when dry, vitreous when wet or polished
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Physical properties
Hardness: 6.5–7 (Mohs scale); Color: Yellowish-brown, mustard, or rust-colored; Luster: Dull or waxy when dry, vitreous when wet or polished; Crystal structure: Trigonal/Microcrystalline; Cleavage: None/Conchoidal fracture; Specific gravity: 2.58–2.91.
Formation & geological history
Formed through the accumulation of fine-grained silica (chalcedony) in pockets of sedimentary or igneous rock. The yellow/brown hue is caused by the presence of iron oxides or goethite. These deposits can range from millions to over a billion years old.
Uses & applications
Used primarily as a gemstone for jewelry, lapidary work (cabochons), interior ornamentation, and as a popular specimen for rock hounds and collectors.
Geological facts
Jasper is an opaque variety of chalcedony. This specific coloration is sometimes called 'Yellow Jasper' or 'Mustard Jasper.' Because it is so hard, it was often used in ancient times for making tools and seals.
Field identification & locations
Identify in the field by its opacity (even when held to light, it doesn't transmit through), its smoothness (waxy feel), and the way it breaks along curved, glass-like surfaces (conchoidal fracture). Commonly found in riverbeds and desert environments.
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