sedimentary
Agate
Silicon dioxide (Chalcedony), SiO2
Hardness: 6.5 to 7 on the Mohs scale. Color: Varies widely including brownish-gray, white, translucent. Luster: Waxy to vitreous. Crystal structure: Trigonal (microcrystalline quartz). Cleavage: None. Specific gravity: 2.58 to 2.64.
- Hardness
- 6
- Color
- Varies widely including brownish-gray, white, translucent
- Luster
- Waxy to vitreous
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Physical properties
Hardness: 6.5 to 7 on the Mohs scale. Color: Varies widely including brownish-gray, white, translucent. Luster: Waxy to vitreous. Crystal structure: Trigonal (microcrystalline quartz). Cleavage: None. Specific gravity: 2.58 to 2.64.
Formation & geological history
Formed mainly within cavities of volcanic and metamorphic rocks through the deposition of silica from groundwater solutions, often in concentric layers over millions of years.
Uses & applications
Used in ornamental objects, jewelry, and polished specimens for lapidary arts.
Geological facts
Agate is one of the most popular stones used in art and jewelry, and its banded varieties have been prized since antiquity for talismans and seals.
Field identification & locations
Can be identified in the field by its waxy luster, conchoidal fracture, and semi-translucent appearance, often found as smooth beach pebbles in coastal or river gravels.
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