Area: 0.5 hectares.
This is a new site, listed in the Geological Conservation Review as of national importance.
Description and Reasons for Notification:
This site shows a superb development of minerals formed by late granitic fractionation and Boron-Fluorine metasomatism in a differentiate of the Belowda coarse megacrystic biotite granite boss.
A short, shallow adit driven westward as part of a larger stockwork tin mine exposes in its walls a topaz-tourmaline-quartz rock. The level is now partly collapsed, but exposures are still visible. Small overgrown dumps at the mouth of the adit also contain large pieces of the topaz-bearing rock. This consists mainly of a fine-grained saccharoidal mixture of topaz and quartz with nests of finely developed tourmaline crystals. Topaz may form up to 80 percent of the rock. Rarely, small yellowish euhedral topaz crystals are present in cavities, the maximum size being 1 cm (the largest recorded in England). The occurrence is very unusual and of considerable mineralogical and petrological interest.