Chalcedony (Blue/Grey Chalcedony)
Microcrystalline Quartz var. Chalcedony · Semi-Precious Gemstone / Mineral Specimen
Crystal System
Trigonal/Monoclinic (Microcrystalline); typically occurs in massive, botryoidal, or nodular habits.
Mineral Group
Silicates (Tectosilicates)
Chemical Formula
SiO2 (Silicon Dioxide)
Formation Process
Hydrothermal or Sedimentary; forms from the deposition of silica-rich fluids at low temperatures in rock cavities, often following volcanic activity.
About This Crystal
A translucent to semi-opaque greyish-blue microcrystalline material with a waxy to vitreous luster. This specimen shows a rough, irregular fracture and is embedded in a brown, iron-stained host rock (matrix).
Physical Characteristics
Color: Pale blue-grey; Streak: White; Cleavage: None; Fracture: Conchoidal to uneven; Specific Gravity: 2.60–2.64; Fluorescence: Often weak yellow-green or blue under UV light.
Optical Properties
Refractive Index: 1.530–1.544; Birefringence: Low (0.004); Pleochroism: None; Optical Character: Aggregates of quartz fibers (doubly refractive).
Hardness & Durability
Origin Region
Globally distributed; notable sources include Brazil, Turkey, Namibia, and the United States (Oregon/California). Typically found in volcanic cavities and sedimentary formations.
Hardness & Durability
Mohs Hardness: 6.5–7.0; Toughness: Very high due to its cryptocrystalline structure; Stable under most conditions but sensitive to strong acids.
Care & Maintenance
Wash with warm soapy water and a soft brush; avoid ultrasonic cleaners if the specimen has visible cracks or porous matrix; store away from harder gems like sapphire or diamond.
Rarity & Value
Common; Value depends on color saturation, translucency, and size. This raw specimen is of modest value, primarily as a collector's mineral or lapidary rough.
Special Characteristics
Displays a waxy luster and 'cloudy' translucency characteristic of silica varieties composed of intergrown quartz and moganite.
Lore & History
Historically used for cameos and seals in Roman and Greek cultures. In folklore, it is considered a stone of communication and brotherhood, associated with the throat chakra.