Amethyst
Ametista
SiO₂ Properties
- Color
- Violet, pale violet, pink-violet
- Luster
- Vitreous
- Density
- 2.65 g/cm³
- Category
- Gem
Amethyst is a violet variety of quartz, colored by the presence of iron and natural irradiation within the crystal lattice. It is the most prized variety of quartz and historically the most used in jewelry, from Roman imperial crowns to medieval episcopal rings.
The violet color derives from the presence of iron (Fe⁴⁺) substituting for silicon in the crystal lattice, combined with natural irradiation. The color intensity varies from pale pink-violet to deep violet. Heat can decolorize amethyst or transform it into citrine.
The bicolor variety with alternating zones of amethyst and citrine within the same crystal is called ametrine and is exclusive to the Anahi mine in Bolivia.
Belongs to the quartz group, trigonal crystal system with a structure of SiO₄ tetrahedral chains. The refractive index is 1.544–1.553, with birefringence of 0.009. Characteristic inclusions include tiger stripes—alternating growth zones—and small crystals of hematite or goethite.
Mining localities
- Minas Gerais, Brasile (principale produttore mondiale)
- Uruguay
- Zambia
- Madagascar
- Magaliesburg, Sud Africa
