White Chalcedony
Quartz var. Chalcedony · Semi-Precious Gemstone / Decorative Stone
Crystal System
Trigonal; Microcrystalline (Cryptocrystalline) aggregate with no visible external crystal faces
Mineral Group
Silicates (Tectosilicate subgroup)
Chemical Formula
SiO2 (Silicon Dioxide)
Formation Process
Sedimentary or Hydrothermal; typically forms at low temperatures through the deposition of silica from groundwater in the cavities of igneous rocks or by replacement in sedimentary layers.
About This Crystal
A small, opaque to translucent white specimen with a waxy to dull luster. The surface appears somewhat weathered or water-worn, showing a typical botryoidal or massive habit. Portions of the stone exhibit faint yellowish or brownish staining from iron oxide impurities.
Physical Characteristics
Color: White to cream; Streak: White; Cleavage: None; Fracture: Conchoidal to splintery; Specific Gravity: 2.6 - 2.64; Tenacity: Brittle; Fluorescence: Often inert, but can show weak green or yellowish fluorescence under UV light.
Optical Properties
Refractive Index: 1.530 - 1.540; Birefringence: Up to 0.009 (often not measurable in cryptocrystalline forms); Pleochroism: None; Optical Character: Doubly Refractive (aggregate).
Hardness & Durability
Origin Region
Global distribution; notable sources include India, Brazil, Madagascar, and various regions of the United States. Frequently found in volcanic basalt cavities and sedimentary environments.
Hardness & Durability
Mohs Hardness: 6.5 - 7.0; Toughness: Very good due to its microcrystalline structure which lacks cleavage planes, making it highly durable for jewelry.
Care & Maintenance
Safe to clean with warm soapy water and a soft brush. While durable, it should be kept away from harsh chemicals like hydrofluoric acid. Can withstand ultrasonic cleaning if no significant internal fractures are present.
Rarity & Value
Common; generally low in price. Value is determined by transparency, uniformity of color, and size. Common treatments include dyeing to produce various colors (though this specimen appears natural).
Special Characteristics
Typically lacks internal phenomena like chatoyancy, but can occasionally show 'ghost' inclusions or a slight blueish opalescence known as adularescence in specific high-quality varieties.
Lore & History
Used since antiquity for cylinder seals in Mesopotamia and cameos in Ancient Greece and Rome. Traditionally considered a 'speaker's stone,' believed to promote calm, balance, and clear communication. Historically used as a protective amulet against 'evil eye' and ill-will.