Quartz
Reference articles are in English.
A quartz crystal from near Llano, Texas, in the GeoDIL geological collection. Source
Description
Quartz is silicon dioxide. It occurs as crystals, massive material and microscopic crystalline varieties, and is a constituent of many rocks. Rock crystal, milky quartz, amethyst and rose quartz are familiar forms. It has a Mohs hardness of 7 and lacks cleavage.
History
Quartz forms in several geological environments. Rock crystal and other coloured hardstones were worked into ornamental objects in Renaissance European workshops, where cutting and polishing developed alongside fitted-stone decoration.
Commissioning
A commission should distinguish natural quartz from quartz-rich rock or a manufactured composite. The proposed piece should be reviewed for colour, inclusions, transparency and any treatments. Abrasive working, the finish and the protection of fine details should be discussed with a specialist.