trigonal Tectosilicates
Amethyst
SiO2:Fe
Quick Facts
Hardness
7.0
Specific Gravity
2.65
Refractive Index
1.544
Optical Character
Uniaxial +
Crystal Structure
#! Species: Amethyst (Quartz)
#! System: Trigonal (32)
#! Habit: Prismatic with angular colour zoning
trigonal[32]:{10-10}@0.5 + {10-11}@1.2 + {01-11}@1.0[colour_zone:angular] | elongate(c:2.0)
trigonal
32
{10-10} {10-11} {01-11}
Physical Properties
Crystal Systemtrigonal
Hardness (Mohs)7.0
Specific Gravity2.65
CleavageNone
FractureConchoidal
LustreVitreous
Optical Properties
Refractive Index1.544
Birefringence0.009
Optical CharacterUniaxial +
Dispersion0.013
Pleochroismweak: Purple / Grey-purple (Subtle; best observed in deeply saturated stones)
Colours
PurpleVioletLilacDeep Siberian purple
Localities
BrazilUruguayZambiaRussiaMadagascar
Common Inclusions
Angular colour zoningBrazil-law twinningTwo-phase fluid inclusionsNegative crystalsGoethite/hematiteTiger stripes (colour banding)
Known Treatments
Heat treatment (to citrine)IrradiationCoating
Crystal Forms
prismrhombohedron_positiverhombohedron_negative
Interactive Preview
Open this crystal in the CDL Playground to rotate, export, and explore in 3D.
Open in Playground #! Species: Amethyst (Quartz)
#! System: Trigonal (32)
#! Habit: Prismatic with angular colour zoning
trigonal[32]:{10-10}@0.5 + {10-11}@1.2 + {01-11}@1.0[colour_zone:angular] | elongate(c:2.0)
Related Minerals
Other minerals in the trigonal system
