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Wheal Coates, St Agnes, St Agnes District, Cornwall, England, UK
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UK Grid Reference: SW700501
Latitude: 50°18'19"N
Longitude: 5°13'49"W
 
 
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 Articles

Pseudomorphous crystals of oxide of tin, found in Huel Coates mine, in St. Agnes by Jolyon & Katya Ralph


Mineral List

Agardite-(Ce)
Andalusite
Arsenopyrite
Bismite
Bismutite
Cassiterite
Cassiterite
var: Wood Tin

Chalcopyrite
Copper
Cuprite
Eulytine
Glauconite
Hematite
Melanterite
Orthoclase
Pyrite
Quartz
Schorl
Svanbergite
Tenorite
'Tourmaline'


21 entries listed. 18 valid minerals. 1 erroneous literature entry.

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References

Rudler, F.W. (1905): A Handbook to a collection of the Minerals of the British Islands, mostly selected from the Ludlam Collection. HMSO Publications (London), 241 pp.

Reid, C., Scrivenor, J.B., Flett, J.S., Pollard, W., and MacAlister, D.A. (1906): The Geology of the Country near Newquay. HMSO Publications (London), 131 pp.

Coon, J. M. (1933): Pseudomorphs of cassiterite, etc., after feldspar at Wheal Coates, St. Agnes, Cornwall. Transactions of the Royal Geological Society of Cornwall 16(6), 297-310.

Dines, H.G. (1956): The metalliferous mining region of south-west England. HMSO Publications (London), Vol. 1, pp. 476-477.

Sharpe, A. & Smith, J. R. (1986): Wheal Coates, St. Agnes: An Archaeological Survey for the National Trust. Conwall Archaeological Unit, Cornwall County Council (Truro).

Clark, A.M., Couper, A.G., Embrey, P.G., and Fejer, E.E. (1986): Waylandite: New Data from an Occurrence in Cornwall, and a Note on 'Agnesite'. Mineralogical Magazine 50, 731-733. [disproves the occurrence of eulytine]

Embrey, P.G., and Symes, R.F. (1987): Minerals of Cornwall and Devon. British Museum of Natural History (London), p. 69.

Rocks & Min. 16, 129.

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Copyright © Jolyon Ralph and Ida Chau 1993-2014. Site Map. Locality, mineral & photograph data are the copyright of the individuals who submitted them. Site hosted & developed by Jolyon Ralph. Mindat.org is an online information resource dedicated to providing free mineralogical information to all. Mindat relies on the contributions of thousands of members and supporters. Mindat does not offer minerals for sale. If you would like to add information to improve the quality of our database, then click here to register.
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