Superficially resembling true diamonds, Killiecrankie ‘diamonds’ are in fact a colourless, variety of topaz. Crystals and water-worn pebbles of topaz are found in abundance in the creeks that flow off the granite of Mount Killiecrankie on Flinders Island, and into Killiecrankie Bay. The colour of the topaz varies from translucent white to pale yellow, pink and blue, and its high lustre led to it becoming known locally as the Killiecrankie diamond.

Topaz is a hard, glassy, aluminium silicate that derives from pegmatitic cavities in granite. Usually forming an ‘orthorhombic’ shape, the crystals are characterised by a perfect basal cleavage and vertically striated prism faces. Topaz crystals of about 20 mm in length are common and some up to 80 mm length have also been reported.

Killiecrankie on Flinders Island was one of the first gem localities discovered in Australia, unearthed in 1810 by New South Wales mineralogist, A.W.H. Humphrey. Humphrey, along with others, sent the gems back to interested collectors in Europe and America. Topaz was also discovered at about the same time (and possibly even preceding the finding at Killiecrankie) in Kent Bay, Cape Barren Island; these minerals were likewise known as ‘Cape Barren diamonds’.