mineral
Sardonyx
Silicon Dioxide (SiO2) with iron oxide impurities
AI-generated identification · may be incorrectHardness: 6.5-7 on Mohs scale; Color: Reddish-brown with white/black bands; Luster: Vitreous to waxy; Crystal Structure: Hexagonal (cryptocrystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.58-2.64.
- Hardness
- 6
- Color
- Reddish-brown with white/black bands
- Luster
- Vitreous to waxy
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Physical properties
Hardness: 6.5-7 on Mohs scale; Color: Reddish-brown with white/black bands; Luster: Vitreous to waxy; Crystal Structure: Hexagonal (cryptocrystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.58-2.64.
Formation & geological history
Formed through the deposition of silica in gas cavities of volcanic rocks, often resulting in distinct parallel bands. Typically found in hydrothermal environments.
Uses & applications
Commonly used in jewelry (rings, pendants), carvings such as cameos and intaglios, and popular in crystal healing and gemstone collecting.
Geological facts
Sardonyx was highly popular in Ancient Rome for making signet rings and seals because hot wax does not stick to it. It has been used for over 4,000 years.
Field identification & locations
Identify by its distinct parallel bands of sard (reddish-brown) and onyx (white or black). Regularly found in Brazil, India, Germany, and Uruguay.
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