Waylandite: new data, from an occurrence in Cornwall, with a note on ‘Agnesite’

Abstract

IN the course of a continuing review of rare minerals that have been reported from the British Isles, we have examined Cornish specimens that purported to be the bismuth silicate, eulytine (Collins, 1881). Two localities are involved: the Restormel (also Royal) iron mine, near Lostwithiel, noted for its remarkable goethite crystals; and Wheal Coates, St Agnes, best known for its pseudomorphs of cassiterite after orthoclase. Collins' specimens, one from each locality (nos. 1588 and 1589, respectively), are in the mineral collection of the Royal Institution of Cornwall, Truro; and another Restormel specimen (BM 32875, Talling no. 614) is in that of the British Museum (Natural History). Specimens from both localities are rather unprepossessing, showing some 'bismuth ochre'. Only on the Restormel material are there a few small, shining crystals, which have proved to be waylandite, a member of the crandallite group; but we have found no eulytine (Macpherson, 1983, p. 249). The dealer Richard Talling, who supplied the BM specimen in 1861, invoiced the crystals as being 'bismuth blende' (= eulytine) and thus seems to be responsible for the original identification, presumably on the basis of appearance and association. A second Talling specimen was acquired as bismutite with the Russell collection (BM 1964R, 7185), and the exact fit of its broken surface shows that if is the 'other half' of BM 32875. It bears the printed number 765, with solid lines above and below, in contrast with the handwritten no. 614; and it is instructive to note that Talling used written numbers for the best specimens he sold, with a different sequence of printed ones for those that he considered less good. The Wheal Coates specimen (RIC no. 1589) has neither waylandite nor eulytine on it, and the earthy mineral gives a clear X-ray powder pattern of bismutite, the basic carbonate of bismuth. Similar material was first examined by the Revd W. Gregor, in about 1809, who supplied the specimen described as an earthy steatite-like mineral and figured in Sowerby's British Mineralogy (Vol. IV, 1811). The status of this material as a carbonate was doubted by Beudant (1832), and later by Greg and Lettsom (1858), but was accepted by Brooke and Miller (1852) who named it agnesite for the locality. It would seem that Gregor (misnamed 'Macgregor'

Eighth supplementary list of British Isles minerals (English)

“…The dendritic gold of Hope's Nose, Torquay, Devon, is palladian, with about 1 to over 6% Pd (Clark and Criddle, 1982); may contain up to 16% of palladium (Scrivener et al, 1982).…”

“…Pdll SO2As2 Cubic Anhedral to euhedral grains (-<15 p.m) associated with gold at Hope's Nose, Torquay, Devon; mertieite-II occurs similarly (Clark and Criddle, 1982 (Moore and Howie, 1984). 'Isostannite' from Cligga Head (Claringbull and Hey, 1955) is krsterite (Kissin and Owens, 1975;Corazza et al, 1986) or ferrok~sterite (Kissin and Owens, 1989 Kidwellite Monoclinic NaFe93+ (PO4)6( OH)10.5H20 Small globules of radiating greenish-yellow fibres, with chalcosiderite in quartz-goethite matrix from Wheal Phoenix, Linkinhorne, Cornwall (Braithwaite and Corke, 1980).…”

“…Zn(OH)2 Tetragonal A new species, from Milltown quarry, near Ashover, Derbyshire; whitish, transparent or translucent, bipyramidal or occasionally tabular crystals up to 1 mm in size, with fluorite, calcite and baryte (Clark et al, 1984;Rust, 1991b). This was the first of four polymorphs of Zn(OH)2 found by S. A.…”

“…Unnamed zinc hydroxide A white radiating acicular mineral, identical with synthetic y-Zn(OH)2, occurs together with other polymorphs of Zn(OH)2 in an oxidised vein exposure at Milltown quarry, near Ashover, Derbyshire (Clark et al, 1988;Rust, 1991b (Frondel, 1952).…”

“…Trigonal (Bi,Ca)A13(PO4,SiO4)2(OH)6 Small (<0.5mm) colourless or brownish crystals, and bluish crystalline bands, on bismutite, Restormel mine, near Lostwithiel, Cornwall (Clark et al, 1986). Tiny greenish blue crystals in cavities in goethite from Stowe's shaft, Wheal Phoenix, Cornwall, belong to the plumbogummite group, near waylandite (NHM identification, 1985, N. Hubbard specimen).…”