Quartz

Quartz is a crystalline form of silica (SiO₂) and is one of the most common gemstones in the world. The name itself comes from the Old English word for "right-angle stone". However, some authorities believe it derives from the Slavic word for "hard". The ancient Europeans believed quartz to be a petrified form of water; hence the name crystalus, from the Greek word for "ice".

Quartz comprises an entire family of gemstones, which are classified according to color:

• rock crystal (clear quartz)
• smoky quartz (also known as morion & caingorm; formerly sold under the trade name "smoky topaz")
• amethyst (purple quartz; also amethyst quartz, which is purple with translucent bands of white quartz)
• citrine (golden yellow to scarlet red quartz; when occuring in the same stone as amethyst, it is known as ametrine)
• rose quartz (translucent quartz that is pale to rose pink in color)

There are also man-made varieties of quartz, such as prasiolite, which is pale green, and blue crystal, a vivid cobalt blue in color.