1911 Encyclopædia Britannica/Cairngorm

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CAIRNGORM, a yellow or brown variety of quartz, named from Cairngorm or Cairngorum, one of the peaks of the Grampian Mountains in Banffshire, Scotland. According to Mr E. H. Cunningham-Craig, the mineral occurs in crystals lining cavities in highly-inclined veins of a fine-grained granite running through the coarser granite of the main mass. Shallow pits were formerly dug in the kaolinized granite for sake of the cairngorm and the mineral was also found as pebbles in the bed of the river Avon. Cairngorm is a favourite ornamental stone in Scotland, being set in the lids of snuff-mulls, in the handles of dirks and in brooches for Highland costume. A rich sherry-yellow colour is much esteemed. Quartz of yellow and brown colour is often known in trade as "false topaz," or simply "topaz." Such quartz is found at many localities in Brazil, Russia and Spain. Much of the yellow quartz used in jewellery is said to be "burnt amethyst"; that is, it was originally amethystine quartz, the colour of which has been modified by heat (see AMETHYST). Yellow quartz is sometimes known as citrine; when the quartz presents a pale brown tint it is called "smoky quartz"; and when the brown is so deep that the stone. appears almost black it is termed morion. The brown colour has been referred to the presence of titanium.