Amethyst
Structure
Amethyst is a violet variety of quartz (SiO2) and owes its violet color to irradiation, impurities of iron (Fe3+) and in some cases other transition metals, and the presence of other trace elements, which result in complex crystal lattice substitutions. The irradiation causes the iron (Fe+3) ions that replace Si in the lattice to lose an electron and form a [FeO4]0 color center. Amethyst is a three-dimensional network of tetrahedra where the silicon atoms are in the center and are surrounded by four oxygen atoms located at the vertices of a tetrahedron. This structure is quite rigid and results in quartz's hardness and resistance to weathering. The hardness of the mineral is the same as quartz, thus making it suitable for use in jewelry.
Hue and tone
Amethyst occurs in primary hues from a light lavender or pale violet to a deep purple. Amethyst may exhibit one or both secondary hues, red and blue. High-quality amethyst can be found in Siberia, Sri Lanka, Brazil, Uruguay, and the Far East. The ideal grade, called "Deep Siberian", has a primary purple hue of around 75–80%, with 15–20% blue and (depending on the light source) red secondary hues. "Rose de France" is defined by its markedly light shade of the purple, reminiscent of a lavender) / lilac) shade. These pale colors were once considered undesirable, but have recently become popular due to intensive marketing.
Hue and tone
Green quartz is sometimes called green amethyst; the scientific name is prasiolite. Other names for green quartz are vermarine and lime citrine.
Reading List
Report Issue