MANGANITE FROM LAVEROCKBRAES, GRANDHOME, ABERDEEN

摘要

Excavations in the late Devensian Banchory Till in the area around NJ 917 111, west of Laverockbraes Farm, about 5 km NNW of the city of Aberdeen, have produced some of the finest specimens of manganite from the British Isles. Lustrous striated prismatic crystals up to about 10 mm in length occur in cavities in massive manganese oxides. The ore was discovered at the beginning of the nineteenth century as an indirect result of canal building. Its principal use appears to have been as a raw material in the production of chlorine bleach. The last definite record of work dates from the 1840s, although anecdotal evidence suggests there may have been a reworking in the last half of the nineteenth century. In 2016, the site was cleared, excavated and landscaped during preparatory work for a large housing development. This provided a unique opportunity to rescue specimens from an area that had been heavily overgrown and inaccessible to mineralogical study for more than a century. The Laverockbraes deposit represents mineralisation deposited by oxidising iron- and manganese-rich fluids in fractures, which locally coalesced to produce ore-grade sections.