Carnelian (Agate)
Chalcedony var. Carnelian · Semi-Precious Gemstone / Collector Mineral
Crystal System
Trigonal (Hexagonal); typically occurs in microcrystalline massive/cryptocrystalline habits
Mineral Group
Silicates (Tectosilicate), Quartz Group
Chemical Formula
SiO2 (Silicon Dioxide with Fe2O3 iron oxide impurities)
Formation Process
Sedimentary/Hydrothermal; formed by the deposition of silica from groundwater in volcanic rock cavities (vesicles) or sedimentary veins at relatively low temperatures
About This Crystal
Deep reddish-orange to brownish-red sphere with translucent to semi-opaque clarity. Features a waxy to vitreous luster and visible concentric 'eye' banding and a thin white mineral vein/fracture fill across the surface
Physical Characteristics
Color: Reddish-brown; Streak: White; Cleavage: None; Fracture: Conchoidal; Specific Gravity: 2.58-2.64; Fluorescence: Weak greenish-white (sometimes inert)
Optical Properties
Refractive Index: 1.530-1.543; Birefringence: up to 0.004; Pleochroism: None; Optical character: Uniaxial positive
Hardness & Durability
Origin Region
Notable sources include India (Gujarat), Brazil, Uruguay, Madagascar, and Botswana; forms in volcanic cavities and sedimentary environments
Hardness & Durability
Mohs Hardness: 6.5 to 7; Toughness: Excellent (no cleavage); Stable under most conditions, though extreme heat can shift color to more red
Care & Maintenance
Clean with warm soapy water and a soft brush; avoid harsh chemicals and ultrasonic cleaners if the stone has surface-reaching fractures/veins; store away from harder stones like diamonds
Rarity & Value
Common; value is determined by color saturation, translucency, and pattern. Typically inexpensive, though specimens with distinct 'eyes' or high translucency are more prized. Often heat-treated to enhance red tones
Special Characteristics
Exhibits concentric color banding (Agate pattern) and a distinct 'eye' centered on the sphere; consistent reddish-brown hue indicates high iron oxide content
Lore & History
Known since the Bronze Age; used in Ancient Egypt for amulets and in Rome for signet rings (due to its non-stick properties with wax). Traditionally associated with the Sacral Chakra, vitality, and courage