Chalcedony
Quartz var. Chalcedony · Semi-Precious Gemstone / Mineral Specimen
Crystal System
Trigonal/Monoclinic (Microcrystalline); typical habit is massive, botryoidal, or as a geode lining.
Mineral Group
Silicates (Tectosilicate)
Chemical Formula
SiO2
Formation Process
Primarily Hydrothermal or Sedimentary; forms from the precipitation of silica-rich fluids at relatively low temperatures in cavities of igneous rocks or through replacement in sedimentary layers.
About This Crystal
A microcrystalline variety of quartz exhibiting a translucent to opaque milky white or bluish-grey body color. It has a waxy to vitreous luster and a smooth, almost gelatinous appearance in fractures.
Physical Characteristics
Color: White to bluish-grey; Streak: White; Cleavage: None; Fracture: Conchoidal to splintery; Specific Gravity: 2.60–2.64; Fluorescence: Sometimes weak green or yellow under UV.
Optical Properties
Refractive Index: 1.530–1.540; Birefringence: Up to 0.004; Pleochroism: None; Optical character: Aggregately polarizes.
Hardness & Durability
Origin Region
Worldwide, notably Brazil, USA (Oregon, Arizona), India, and Madagascar. Common in volcanic and sedimentary environments.
Hardness & Durability
Mohs hardness: 6.5–7; Toughness: Very high due to its microcrystalline structure; Stability: Excellent, resistant to most household chemicals except hydrofluoric acid.
Care & Maintenance
Safe to clean with warm soapy water and soft brushes. Sensitive to excessive heat which may dry out more porous varieties, potentially causing color change.
Rarity & Value
Very common; value is determined by color uniformity, translucency, and size. Fine blue or lavender varieties are more prized. Treatments like dyeing are very common.
Special Characteristics
Can show a slight bluish opalescence (Tyndall scattering). Some specimens contain 'enhydros' (trapped water bubbles) or dendritic inclusions.
Lore & History
Historically used for seals, cameos, and beads by Roman and Greek civilizations. Traditionally associated with the throat chakra and believed to promote brotherhood and goodwill.