mineral
Chalcedony (Agate / Chert nodule)
Microcrystalline Quartz (SiO2)
AI-generated identification · may be incorrectHardness: 6.5-7 on Mohs scale. Color: Honey-brown, amber to caramel with semi-translucent body. Luster: Waxy to vitreous. Crystal system: Trigonal/microcrystalline. Fracture: Conchoidal. Cleavage: None. Specific gravity: 2.58-2.64.
- Hardness
- 6
- Color
- Honey-brown, amber to caramel with semi-translucent body
- Luster
- Waxy to vitreous
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Physical properties
Hardness: 6.5-7 on Mohs scale. Color: Honey-brown, amber to caramel with semi-translucent body. Luster: Waxy to vitreous. Crystal system: Trigonal/microcrystalline. Fracture: Conchoidal. Cleavage: None. Specific gravity: 2.58-2.64.
Formation & geological history
Formed by precipitation of silica from groundwater or low-temperature hydrothermal fluids inside cavities of sedimentary rocks (limestone/chalk) or volcanic vesicles. Often weathered out as alluvial or river-tumbled pebbles.
Uses & applications
Commonly collected as lapidary rough, tumbled into decorative gemstones, carved, and historically used for stone tools and arrowheads due to sharp conchoidal fracturing.
Geological facts
Chalcedony is composed of microscopic intergrowths of quartz and moganite. Translucent, honey-colored varieties found in river gravels are often referred to as 'carnelian chalcedony' or water-worn agates.
Field identification & locations
Identify in the field by its distinct waxy luster, smooth water-worn texture, conchoidal fracture scars, high hardness (easily scratches glass, cannot be scratched by a steel nail), and translucency when backlit. Commonly found in riverbeds, gravel bars, and desert washes worldwide.
