Loch a' Sgurr Pegmatite
Condition (NatureScot)
| Unit | Feature | Condition | Area (ha) | Assessed |
|---|---|---|---|---|
| F1 | Mineralogy of Scotland | Favourable | — | 2005-03-31 |
Geology & landscape
Rock Type: Gneiss, Granite
Landscape processes: Volcanic / Igneous
Description
Loch a' Sgurr Pegmatite Loch a’ Sgurr Pegmatite SSSI is a small exposure of pegmatite situated in the Bays of South Harris, south of Fionnsabhagh. Pegmatite is a very coarsely grained variety of granite. The site excellently exposes white albitic plagioclase and quartz, and is complementary to those at Chaipaval and Sletteval. Magnetite segregations up to 15 cm in length are associated with green mica. These segregations contain the radioactive minerals uraninite, thorite and monazite and the surrounding feldspar is reddened by radioactivity. Coatings of yellow uranophane are visible on the surface. Accessory minerals such as spessartine, garnet, allanite, epidote and zircon are present. The presence of magnetite rather than mica, and albite rather than potash feldspar, indicate that this pegmatite is rather more basic than those normally found in acid gneiss terrains.