Chalcedony (Agate/Druzy Quartz)
Quartz var. Chalcedony / Crystalline Quartz · Mineral Specimen / Semi-Precious Gemstone
Crystal System
Trigonal/Hexagonal; typically microcrystalline (cryptocrystalline) or forming as tiny druzy pyramidal crystals in cavities.
Mineral Group
Silicates (Tectosilicate)
Chemical Formula
SiO2 (Silicon Dioxide)
Formation Process
Hydrothermal and Sedimentary; forms via the deposition of silica-saturated fluids in rock cavities at relatively low temperatures.
About This Crystal
The specimen shows a translucent to opaque milky-white to light blue-grey chalcedony base with areas of sparkling crystalline 'druzy' quartz. It features a weathered, brownish-yellow iron-stained matrix or rind.
Physical Characteristics
Color: White, grey, yellow-brown; Streak: White; Cleavage: None; Fracture: Conchoidal to uneven; Specific Gravity: 2.6 - 2.65; Fluorescence: Often inert, but can show dull green or white under shortwave UV.
Optical Properties
Refractive Index: 1.544-1.553; Birefringence: 0.009; Luster: Vitreous on crystal faces, waxy to dull on the chalcedony/matrix surfaces; Diaphaneity: Translucent to opaque.
Hardness & Durability
Origin Region
Global; notably Brazil, Uruguay, India, and the USA. Found in volcanic cavities (geodes) and sedimentary host rocks.
Hardness & Durability
Mohs Hardness: 6.5 to 7; Toughness: Very Good (due to microcrystalline structure); Stability: Stable, though porous varieties can absorb chemicals.
Care & Maintenance
Clean with warm soapy water and a soft brush; avoid harsh chemicals or high heat. Ultrasonic cleaners are generally safe for solid pieces but use caution with fragile druzy surfaces.
Rarity & Value
Common; value is determined by aesthetic formation, color, and crystalline sparkle rather than rarity. Generally affordable as collector mineral specimens.
Special Characteristics
Druzy texture (a coating of fine crystals), micro-pitting, and iron-oxide staining creating natural 'naturalist' color palettes.
Lore & History
Historically used for cameos and seals. In traditional lore, chalcedony is associated with balance and calm; druzy quartz is often believed to amplify energy and promote group harmony.