SiO2 (Fe bearing)Trigonal
Amethyst
SiO2 (Fe bearing)
SilicatesChemical FormulaSiO2 (Fe bearing)
Crystal SystemTrigonal
Mohs Hardness7
Specific Gravity2.65
ColorPurple, violet
LusterVitreous
StreakWhite
CleavageNone
FractureConchoidal
Occurrence
Purple variety of quartz. Color caused by iron impurities and irradiation.