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Wheal Coates, St Agnes, St Agnes District, Cornwall, England, UK

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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 Articles

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

Mineral List

18 valid minerals. 1 erroneous literature entry.


Geologic TimeRocks, Minerals and Events
ⓘ Major polymetallic mineralization~270 MaCornwall, England, UK
ⓘ Porphyry dikes intruded (latest age)~275 MaCornwall, England, UK
ⓘ Greisenization (latest age)~280 MaCornwall, England, UK
ⓘ Porphyry dikes intruded (earliest age)~280 MaCornwall, England, UK
ⓘ Formation of metallized pegmatites~285 MaCornwall, England, UK
ⓘ Greisenization (earliest age)~285 MaCornwall, England, UK
ⓘ Emplacement of major plutons~295 MaCornwall, England, UK

Regional Geology

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

Middle Devonian
382.7 - 393.3 Ma

ID: 2035678
Middle Devonian (Undifferentiated)

Age: Middle Devonian (382.7 - 393.3 Ma)

Lithology: Mudstone, siltstone and sandstone

Reference: British Geological Survey. DiGMapGB-625. British Geological Survey ©NERC. [23]

Data and map coding provided by, used under Creative Commons Attribution 4.0 License

This page contains all mineral locality references listed on This does not claim to be a complete list. If you know of more minerals from this site, please register so you can add to our database. This locality information is for reference purposes only. You should never attempt to visit any sites listed in without first ensuring that you have the permission of the land and/or mineral rights holders for access and that you are aware of all safety precautions necessary.


Sort by Year (asc) | by Year (desc) | by Author (A-Z) | by Author (Z-A)
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. Cornwall 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 & Minerals 16, 129.

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