Minerals

Cairngorm: a semi-precious stone, consisting of crystals of smoky quartz

In the Victorian era, the collection of Scottish gemstones was fashionable and much effort was expended in the hunt for the attractive Cairngorms. This is a quartz crystal coloured by a variable iron content, giving smoky yellow to dark brown and even black hues. The Cairngorms are associated with fissures at the centre of aplite or pegmatite veins. At a late stage in the cooling of the granite, these fissures were filled with supersaturated residual fluids in which large crystals were able to grow.

The most easily accessible and obvious locations for Cairngorms were mined by hand in the 19th century to depths of up to 2 m. Small examples can sometimes be found in the surface float or on scree slopes but the best examples recovered in recent years came from the excavations for the funicular railway.

Crystals of greenish beryl and pale blue topaz have also been recovered from the Cairngorms.