Agate
Quartz var. Agate (Microcrystalline Quartz) · Semi-Precious Gemstone / Mineral Specimen
Crystal System
Trigonal symmetry but microcrystalline; habits include banded, botryoidal, and massive nodules
Mineral Group
Silicates (Tectosilicate group)
Chemical Formula
SiO2 (Silicon Dioxide) often with iron or manganese inclusion layers
Formation Process
Hydrothermal formation within volcanic rock vesicles or sedimentary cavities where silica-rich groundwater precipitates over time
About This Crystal
Translucent to opaque microcrystalline texture featuring concentric or moss-like banding; exhibits vitreous to waxy luster with colors ranging from earthy reds and browns to bluish-grey centers
Physical Characteristics
Color: Red, brown, grey-blue; Streak: White; Cleavage: None; Fracture: Conchoidal; Specific Gravity: 2.58–2.64; Fluorescence: Variable, sometimes pale green or yellow
Optical Properties
Refractive Index: 1.544–1.553; Birefringence: 0.009; No pleochroism; Aggregates are typically doubly refractive
Hardness & Durability
Origin Region
Brazil, Uruguay, Lake Superior (USA), and India; commonly found in volcanic and metamorphic rock cavities
Hardness & Durability
Mohs Hardness: 6.5–7.0; Toughness: High (very durable due to interlocking structure); Stability: Generally stable, but sensitive to extreme heat
Care & Maintenance
Clean with warm soapy water; avoid ultrasonic cleaners if the stone is dyed; store away from harder gems like diamond or sapphire
Rarity & Value
Common; Value based on banding patterns, size, and color saturation; higher value for 'fortification' or 'eye' patterns
Special Characteristics
Banding (concentric or parallax), translucent edges, and occasional botryoidal 'grape' habits or geodes in the center
Lore & History
Historically used for amulets in Ancient Egypt and Babylonia; traditionally believed to provide balance, protection, and emotional grounding in various cultures