Rock Identifier
Yellow Chalcedony (Agate/Carnelian variant) (Silicon Dioxide (SiO₂)) — mineral
mineral

Yellow Chalcedony (Agate/Carnelian variant)

Silicon Dioxide (SiO₂)

Hardness: 6.5-7 on Mohs scale; Color: Semi-translucent yellow to honey-brown; Luster: Waxy to vitreous; Crystal Structure: Cryptocrystalline (hexagonal system); Cleavage: None (conchoidal fracture); Specific Gravity: 2.58-2.64

Hardness
6
Color
Semi-translucent yellow to honey-brown
Luster
Waxy to vitreous
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Physical properties

Hardness: 6.5-7 on Mohs scale; Color: Semi-translucent yellow to honey-brown; Luster: Waxy to vitreous; Crystal Structure: Cryptocrystalline (hexagonal system); Cleavage: None (conchoidal fracture); Specific Gravity: 2.58-2.64

Formation & geological history

Formed through the deposition of silica-rich fluids in volcanic cavities (vugs) or sedimentary fissures. Most specimens are derived from Cenozoic volcanic activity, typically occurring in basaltic or rhyolitic host rocks.

Uses & applications

Used primarily for lapidary work, jewelry (beads, cabochons), carvings, and as a collector's specimen. In industry, it was historically used for mortar and pestles due to its toughness and chemical resistance.

Geological facts

In ancient times, yellow and red chalcedonies were believed to ward off 'evil spirits' and were popular for wax seals because the wax wouldn't stick to the smooth, waxy surface of the stone.

Field identification & locations

Identify in the field by its semi-translucent nature and smooth, 'waxy' texture compared to opaque rocks. It will scratch a piece of glass but cannot be scratched by a steel knife. Common in riverbeds and arid desert pavements globally, particularly in the western USA (Oregon/California) and Brazil.

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