Tacharanite

Tacharanite occurs in nature as bundles and spherules of silky white fibres in altered basalts. It's found in several locations around the world but the 'type' locality (where it was first found) is a road cutting about 1km North of Portree on the Isle of Skye. Very romantic!

A hydrated calcium aluminium silicate, tacharanite has the chemical formula Ca₁₂Al₂Si₁₈O₅₁.18H₂O. While the vast majority of mineral names are derived from a personal name or a place name, the name of this mineral does not. The name was chosen by the author of the original paper, Jessie Sweet (1901 – 1979), then of the British Museum (Natural History). But she also briefly worked at the Royal Scottish Museum (as we were once called). 

Tacharanite illustration by Vojta Hýbl.

The first part of the name, 'tacharan', is a Scottish Gaelic word: tàcharan, meaning a changeling (in Scottish and Irish folklore, a changeling was the child of a fairy, troll or sprite that had been swapped for a human child). The mineral was named this in recognition of the fact that the mineral alters on exposure to air to two different minerals: tobermorite (note another Scottish connection here) and gyrolite. Sweet also wanted to recognise the wealth of folk history and stories of the Scottish Highlands and Islands. Read more about Jessie Sweet.

Silky white fibres of tacharanite from the Isle of Skye.

The road north from Portree has many road cuttings old and new and it's difficult to know which one was used by Jessie. Her original paper of 1961 says it's half a mile (800m) north of Portree on the Staffin Road (A855). Today this area has been largely built over. The specimen in the image above was collected by Peter Davidson and Brian Jackson of the Department of Natural Sciences in the late 1980s from a locality a little bit further north at Lealt. This location is famous for the waterfalls but also for the Lealt Diatomite Railway.

Lealt Waterfalls.

Diatomite is a silica rich sediment found on Skye at the bottom of Loch Cuithir (15 km North of Portree). It was extracted, dried and sent to the coast at Invertote over a narrow-gauge railway to be shipped out for processing. The dried material was then mixed with nitro-glycerine to form dynamite. Some evidence of the railway and workings remain, but very little.