Chalcedony
Microcrystalline Quartz var. Chalcedony · Semi-Precious Gemstone / Mineral Specimen
Crystal System
Trigonal (Monoclinic sub-microscopic); typically cryptocrystalline or botryoidal habit
Mineral Group
Silicates (Tectosilicate subgroup)
Chemical Formula
SiO2 (Silicon Dioxide) with trace iron impurities
Formation Process
Sedimentary or Hydrothermal; forms from the deposition of silica from water solutions in volcanic cavities or sedimentary rocks.
About This Crystal
This specimen exhibits a waxy to dull luster, translucent to opaque body, and a creamy-beige to tan color. It shows a characteristic pitted, weathered surface texture often found in alluvial or beach-worn nodules.
Physical Characteristics
Color: Cream/Tan; Streak: White; Cleavage: None; Fracture: Conchoidal to uneven; Specific Gravity: 2.6-2.64; Luster: Waxy to vitreous; Fluorescence: Often inert but can show green under UV.
Optical Properties
Refractive Index: 1.530-1.543; Birefringence: Up to 0.004; Pleochroism: None; Optical Nature: Aggregate; typically lacks strong optical phenomena in this raw state.
Hardness & Durability
Origin Region
Global distribution; notable sources include Brazil, Uruguay, India, and various river beds worldwide.
Hardness & Durability
Mohs Scale: 6.5-7.0; Toughness: Very High due to its microcrystalline fibrous structure; Stability: Excellent, resistant to most household chemicals.
Care & Maintenance
Safe to clean with warm soapy water and soft brushes. Generally resistant to ultrasonic cleaning, though should be kept away from hydrofluoric acid.
Rarity & Value
Common; value is generally low for raw nodules, increasing based on color saturation, translucency, and the presence of unique patterns like banding (agate) or inclusions.
Special Characteristics
Exhibits a 'desert varnish' or weathered cortex; notable for its extreme toughness and lack of cleavage planes making it ideal for lapidary work.
Lore & History
Historically used for cylinder seals in Mesopotamia and tool making due to its durability. Symbolically associated with stability, grounding, and nurturing energies in modern crystal lore.