Wheal Coates, St Agnes, St Agnes District, Cornwall, England, UK
|Latitude & Longitude (WGS84):||50° 18' 19'' North , 5° 13' 49'' West|
|Latitude & Longitude (decimal):||50.30528,-5.23028|
|UK National Grid Reference:||SW700501|
|Other regions containing this locality:||Devon and Cornwall metalliferous mining district, England, UK|
|Köppen climate type:||Cfb : Temperate oceanic climate|
The mine is famous for the highly desirable and classic pseudomorphs after Carlsbad twins of orthoclase feldspar that were found around 1828. The replacing material consists of a granular mixture of largely cassiterite and minor quartz in varying proportions. Depending on the fraction of cassiterite, the colour varies from almost black to various shades of grey. The vein where they came from (perhaps an elvan), only 3 inches wide on average, was in a soft decomposed granite and contained so much of a light red sandy matter that it was called "the sand lode" (Coon, 1933; Rudler, 1905; Reid et al., 1906).
The pseudomorphs are typically are around 2.5 cm long or less, but specimens to a maximum of 5.6 cm are known. Good examples are rare and fakes were made in the 19th century by coating appropriately shaped lead sheet with granular cassiterite (Embrey & Symes, 1987). Elsewhere, similar pseudomorphs have been found very rarely at Carn Brea Mine, Illogan and at Balleswidden Mine, St. Just (Rudler, 1905).
Mindat ArticlesPseudomorphous crystals of oxide of tin, found in Huel Coates mine, in St. Agnes by Jolyon & Katya Ralph
18 valid minerals. 1 erroneous literature entry.
|Geologic Time||Rocks, Minerals and Events|
This geological map and associated information on rock units at or nearby to the coordinates given for this locality is based on relatively small scale geological maps provided by various national Geological Surveys. This does not necessarily represent the complete geology at this locality but it gives a background for the region in which it is found.
Click on geological units on the map for more information. Click here to view full-screen map on Macrostrat.org
382.7 - 393.3 Ma
|Middle Devonian (Undifferentiated)|