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.