sedimentary
Yellow Chalcedony (Agate)
Silicon Dioxide (SiO2)
Hardness: 6.5-7 Mohs; Color: Pale yellow to deep amber (translucent); Luster: Waxy to vitreous; Crystal Structure: Cryptocrystalline (Trigonal/Monoclinic); Cleavage: None; Specific Gravity: 2.58–2.64
- Hardness
- 6
- Color
- Pale yellow to deep amber (translucent)
- Luster
- Waxy to vitreous
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Physical properties
Hardness: 6.5-7 Mohs; Color: Pale yellow to deep amber (translucent); Luster: Waxy to vitreous; Crystal Structure: Cryptocrystalline (Trigonal/Monoclinic); Cleavage: None; Specific Gravity: 2.58–2.64
Formation & geological history
Formed through the deposition of silica from groundwater in cavities of igneous rocks or sedimentary layers. It can be found in volcanic vugs or as nodules in limestone.
Uses & applications
Used primarily in lapidary work for jewelry, cabochons, and decorative carvings. Industrially, it has been used in mortar and pestle sets due to its hardness and durability.
Geological facts
Chalcedony is a cryptocrystalline form of silica, meaning its crystals are too small to be seen with a microscope. It has been used for making tools and seals since the Bronze Age.
Field identification & locations
Identify by its waxy luster, conchoidal fracture, and translucency when held to light. Frequently found in riverbeds or volcanic regions like Brazil, India, and the Western United States.
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