trigonal Tectosilicates
Amethyst
SiO2:Fe
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}
Quick Facts
Hardness
7.0
Specific Gravity
2.65
Refractive Index
1.544
Optical Character
Uniaxial +
Interactive Preview
Open this crystal in the CDL Playground to rotate, export, and explore in 3D.
Open in PlaygroundPhysical 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 PlaygroundRelated Minerals
Other minerals in the trigonal system
