Carnelian Agate
Quartz (Silicon Dioxide) var. Carnelian · Semi-Precious Gemstone / Mineral Specimen
Crystal System
Trigonal / Hexagonal; Microcrystalline or Cryptocrystalline habit (fibrous chalcedony structure)
Mineral Group
Silicates; Tectosilicate (Quartz group)
Chemical Formula
SiO2 with Fe2O3 (Iron Oxide) impurities providing the red-orange coloration
Formation Process
Hydrothermal or Sedimentary; forms through the deposition of silica-rich fluids in volcanic cavities or rock fissures at low to moderate temperatures.
About This Crystal
The specimen shows an earthy, semi-translucent to opaque appearance with variegated tones of russet red, brownish-orange, and pale tan. It exhibits a waxy to dull vitreous luster on its irregular, weathered surface.
Physical Characteristics
Color: Reddish-brown; Streak: White; Cleavage: None; Fracture: Conchoidal to uneven; Specific Gravity: 2.58-2.64; Fluorescence: Usually inert but may show weak yellow-green under SWUV.
Optical Properties
Refractive Index: 1.530-1.540; Birefringence: Up to 0.009 (often not measurable in cryptocrystalline forms); Optical Character: Uniaxial positive; No pleochroism.
Hardness & Durability
Origin Region
Brazil, India, Madagascar, and Uruguay. Commonly found in basaltic rocks and sedimentary gravels.
Hardness & Durability
Mohs Hardness: 6.5 to 7. Toughness: High (due to fibrous structure), making it very durable for jewelry and carvings.
Care & Maintenance
Safe to clean with warm soapy water. Resistant to most household chemicals, but prolonged exposure to high heat may deepen color or cause fracturing.
Rarity & Value
Common; Value is driven by color saturation and translucency. Heat treatment of brownish chalcedony to enhance red tones is a standard industry practice.
Special Characteristics
May exhibit color zoning or banding consistent with agate-type structures; the red color is specifically attributed to hematite inclusions.
Lore & History
Used since the Neolithic period for beads and seals. In ancient Egypt, it was known as the 'setting sun' and used in protective amulets. Traditionally associated with vitality and the sacral chakra.