mineral
Chalcedony (Agate/Chert variety)
Silicon Dioxide (SiO2)
AI-generated identification · may be incorrectHardness: 6.5-7 (Mohs); Color: Grayish-blue, milky white, tan crust; Luster: Waxy to vitreous; Crystal Structure: Trigonal (microcrystalline/cryptocrystalline); Cleavage: None; Fracture: Conchoidal; Specific Gravity: 2.58-2.64.
- Hardness
- 6
- Color
- Grayish-blue, milky white, tan crust
- Luster
- Waxy to vitreous
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Physical properties
Hardness: 6.5-7 (Mohs); Color: Grayish-blue, milky white, tan crust; Luster: Waxy to vitreous; Crystal Structure: Trigonal (microcrystalline/cryptocrystalline); Cleavage: None; Fracture: Conchoidal; Specific Gravity: 2.58-2.64.
Formation & geological history
Formed through the deposition of silica from groundwater in volcanic rock cavities or sedimentary environments. This specimen shows a botryoidal (grape-like) texture in the vug and a weathered host-rock crust.
Uses & applications
Used primarily for lapidary work, jewelry (cabochons), and as a collector's specimen. Historically used for making stone tools due to its conchoidal fracture.
Geological facts
Chalcedony is a cryptocrystalline form of silica, meaning its crystals are too small to be seen under a normal microscope. It forms the basis for many gemstones including agate, jasper, and carnelian.
Field identification & locations
Identify by its waxy luster, hardness (it will scratch glass), and its lack of visible crystal faces despite being translucent. Found globally in volcanic regions and sedimentary beds.
