Amethyst
Quartz var. Amethyst · Semi-Precious Gemstone
Crystal System
Trigonal; typically occurs as hexagonal prisms terminated by two sets of rhombohedrons
Mineral Group
Silicates (Tectosilicate)
Chemical Formula
SiO2 (Silicon Dioxide) with trace amounts of iron (Fe3+) and irradiation
Formation Process
Hydrothermal crystallization from silica-rich fluids in volcanic rock cavities (geodes) or hydrothermal veins
About This Crystal
Transparent to translucent purple quartz variety; displays vitreous luster and typically shows color zoning from pale lilac to deep violet
Physical Characteristics
Color: light to dark purple; Streak: white; Cleavage: none; Fracture: conchoidal; Specific Gravity: 2.65; Fluorescence: typically inert
Optical Properties
Uniaxial positive; Refractive Index: 1.544-1.553; Birefringence: 0.009; Weak pleochroism in purple shades
Hardness & Durability
Origin Region
Brazil (Rio Grande do Sul), Uruguay, Zambia, Madagascar, and Russia; often found in volcanic geodes
Hardness & Durability
Mohs hardness: 7; Good toughness / no cleavage; highly durable for daily jewelry wear
Care & Maintenance
Avoid prolonged sunlight (can fade); wash with warm soapy water; avoid sudden temperature changes or high heat
Rarity & Value
Common; value increases with color saturation and lack of visible inclusions; typically $2-$50 per carat depending on quality
Special Characteristics
Color zoning (tiger stripes), fluid inclusions, and iron-induced color that can be altered by heat to produce citrine
Lore & History
Ancient Greeks believed it prevented intoxication (amethystos: 'not drunk'); historically used in royal jewelry and as a stone of spiritual protection