Quartz is the name given to a crystalline rock composed of silicon dioxide. It is extremely common, being the most abundant single mineral on earth. It makes up about 12% of the earth’s crust, occurring in a large variety of igneous, metamorphic and sedimentary rocks. There are innumerable varieties of quartz, a number of which are gemstones – some of these varieties are very rare. Generic ‘quartz’ is usually colourless or white, and its crystals are transparent to translucent.
Chalcedony is a type of quartz, and onyx, agate and carnelian are types of chalcedony. Other varieties of quartz include amethyst, which is purple, [citrine which is yellow, rose quartz which is pink, and smoky quartz, which is soft brown. As can be seen from this list, the characteristics of quartz are almost infinite – it comes in nearly every colour of the spectrum, some stones are banded, some are nearly opaque, others transparent and so on. Thus it is used abundantly in fine and designer jewellery.
The Roman naturalist Pliny the Elder believed that quartz was permanently frozen ice. This belief may have originated with the same Greek belief, that it was the gods who had frozen it. Pliny’s independent reasoning behind this was that quartz is found near glaciers in the Alps and large crystals of quartz were fashioned into spheres to cool the hands. He also observed that quartz split light into a spectrum and likened this to what he saw in ice.
The name "quartz" comes from the German quarz, which is of Slavic origin and means simply ‘rock crystal’. The Irish word for quartz is grian cloch, which means 'stone of the sun'.