Amethyst

Quartz is one of the most widespread minerals and the one with the most varieties. These are divided into two main groups, depending on whether they are minerals with clearly visible crystals or minerals formed by aggregates of microscopic crystals. The first group includes pure quartz (hyaline quartz or rock crystal), colourless and transparent, amethyst quartz, smoky quartz or morion, citrine quartz, blue quartz, iris quartz and rose quartz, varieties coloured by impurities. The second group, on the other hand, includes chalcedony (which in turn comprises carnelian, agate and onyx), jasper and flint.

What distinguishes amethyst from the other varieties of quartz is its violet colour and the greater development of the terminal pyramids. At a temperature of 400-500 °C amethysts become citrine quartz. Amethyst crystals form essentially inside geodes in basaltic rocks.

The main use of amethyst is in gemmology. Varieties with a clear, intense colour are cut into oval or rounded shapes, with faceted cuts, often brilliant-cut.