Agate
Chalcedony var. Agate · Semi-Precious Gemstone, Collector Mineral
Crystal System
Trigonal crystal system, often occurring in microcrystalline or cryptocrystalline massive habits with concentric banding
Mineral Group
Silicates; Tectosilicate (Quartz group)
Chemical Formula
SiO2 (Silicon Dioxide) with traces of Iron, Magnesium, Manganese, and Chromium
Formation Process
Sedimentary and Hydrothermal; forms as a primary or secondary mineral through silica deposition from groundwater in cavities within volcanic or metamorphic rocks
About This Crystal
Polished tumbled stone showing characteristic concentric and wavy banding; colors range from translucent grays and greens to earthy browns and white; vitreous to waxy luster; translucent to opaque
Physical Characteristics
Color: multicolored banding; Streak: White; Cleavage: None; Fracture: Conchoidal; Specific Gravity: 2.58-2.64; Fluorescence: Variable, sometimes glows faint yellow or green under UV
Optical Properties
Refractive Index: 1.530-1.544; Birefringence: up to 0.004; no pleochroism; generally aggregate polarization
Hardness & Durability
Origin Region
Notably Brazil, Uruguay, India, and Madagascar; typically found in volcanic cavities (geodes) or as stream-rolled pebbles
Hardness & Durability
Mohs Hardness: 6.5-7; Toughness: Excellent (highly resistant due to cryptocrystalline structure); high wearability for jewelry
Care & Maintenance
Clean with warm soapy water and a soft brush; avoid harsh chemicals and extreme heat; generally stable in sunlight but dyed specimens may fade
Rarity & Value
Common to Uncommon; value determined by pattern complexity and color contrast; inexpensive as tumbled stones; common treatments include dyeing and heat treatment
Special Characteristics
Exhibits distinctive 'lace' or orbital banding; may contain moss-like or dendritic inclusions; often polished to a high vitreous shine
Lore & History
Historically used in ancient Egypt and Sumer for amulets and cylinder seals; traditionally associated with grounding, protection, and stabilizing energy in various cultures