mineral

Yellow Chalcedony (Agate)

Silicon Dioxide (SiO2)

Hardness: 6.5–7 on Mohs scale; Color: Translucent yellow to honey-orange; Luster: Waxy to vitreous; Crystal structure: Trigonal (microcrystalline/cryptocrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6–2.64.

Hardness: 6
Color: Translucent yellow to honey-orange
Luster: Waxy to vitreous

Identified March 15, 2026More mineral →

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Physical properties

Formation & geological history

Formed from silica-rich groundwater depositing in cavities of volcanic rocks or sedimentary formations. Most specimens range from a few million to over 100 million years old, often found in amygdaloidal basalts.

Uses & applications

Commonly used in lapidary arts for cabochons, beads, and carvings. Historically used for seals and amulets. Also used in industrial applications for its hardness as a grinding media.

Geological facts

Yellow chalcedony is often marketed as 'Yellow Agate' even when it lacks distinctive banding. It is a variety of quartz that consists of microscopic crystals that cannot be seen individually.

Field identification & locations

Identify in the field by its waxy luster, translucency when held to light, and lack of visible crystals. Commonly found in riverbeds, desert pavements, and volcanic outcrops in Brazil, India, and the Western United States.