Smoky yellow to smoky brown, often gray and black, are the tints of the cairngorm. This species of transparent quartz takes its name from Cairngorm in Invernessshire, in Scotland, a locality where some of the best specimens have been found. Pike’s Peak, Arkansas, and certain districts in North Carolina have also produced some very fine smoky topazes.

The cairngorm is used for seals, beads, and some of the cheaper jewels, and is largely sold at watering-places in Switzerland, and in the Western United States.

The stone is very popular in Scotland. Hair or needle stones is the name given to these varieties of crystallized quartz when they contain foreign substances, such as rutile, manganese, chlorite, etc., in hair or needle formation.

These stones are cut to represent the needle enclosures in an upright position, and are called sagenite or Venus hair stones or love arrows.

Iridescent or rainbow quartz is the variety of rock-crystal containing cracks and fissures which reflect all the colors of the rainbow. Quartz can also be artificially colored by rapidly cooling a heated specimen and then dipping the piece into a coloring preparation; the minute cracks in the quartz absorb the coloring matter, and the result is a red-, blue-, or green-tinted stone.

The massive varieties of quartz embrace the rose quartz, avanturine, cat’s-eye, crocidolite, heliotrope, chrysoprase, prase, plasma, chalcedony, agates, onyx, carnelian, jasper, hornstone, and flint.