Wavellite from Devon, southwest England

--- historical occurrence of an unusual phosphate mineral

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Figure 1. Radiating, spheroidal or discoidal masses of a pale white to brown phosphate, wavellite, on a fine-grained granular sandstone or siltstone host rock. Each of the nicely developed, colour-zoned aggregates is 10-12 mm in diameter, displaying a bladed or acicular habit and a silky lustre. A sample from my youth, presumably collected significantly pre-1960, my original number 42.74.1. The location is the Barnstaple (often mis-spelled as Barnstable) area of the county of Devon (see below for details). It generally occurs as spheres up to 1 cm - and rarely to 5 cm - in diameter, that may be blackened by carbonaceous inclusions (Embrey and Symes, 1987, p.126).


"Rock of the Month #199, posted for January 2018" ---

Wavellite

is an hydrated, orthorhombic phosphate of aluminium, ideal formula Al3(PO4)2(OH,F) 3.5H2O. It has been identified from a variety of locations for over two centuries, First described in 1805, the type locality has been described as Barnstaple, a former river port and centre of the woolen trade, situated at the head of an estuary on the north coast of Devon, in southwest England. Phosphates such as wavellite, apatite and vivianite featured in early mineralogy texts of the 19th century (e.g., Varley, 1849) and in British topographical mineralogy works (Greg and Lettsom, 1858; Collins, 1892; Heddle, 1901; also Russell et al., 1948; Embrey and Symes, 1987). Wavellite is also figured in a number of modern mineral guides (a selection includes Metz, 1965; Pough, 1970, 1996; Hofmann and Karpinski, 1981; Kourimsky, 1995; Bonewitz, 2005; Thomas, 2008). It is named for Dr William Wavell, who found an early, if not perhaps the first specimen of the mineral.

In terms of teaching texts, members of the apatite family are naturally the most common species of phosphates that a student may encounter. However, wavellite does figure in a few advanced texts (e.g., Melgarejo and Martin, 2011). Although it is a rather delicate mineral, Moh's hardness just 3.5 to 4, wavellite is occasionally used in jewellery (Thompson, 2011; Erickson, 2011).

The type locality

Arthur Kingsbury (1964, pp.254-256) investigated the exact location of the material for the original description, which had been figured in Sowerby's "British Mineralogy", volume 2 (1806) **. The type material was apparently collected circa 1785, at "Barnstaple". The actual locality is closer to South Molton, E.S.E. of Barnstaple, on the southwest flank of Exmoor National Park. The locality lies in the western portion of High Down quarry, in West Buckland parish. Kingsbury visited the quarry in 1945 and was able to collect typical wavellite, some of which contains small spherules of variscite, which occur also in the host black slate. The host rocks are deposits of the upper Carboniferous-age Culm sedimentary basin. The Culm strata include turbiditic siltstones and sandstones, chert and shales. Kingsbury also notes other Cornish occurrences of wavellite, in the St. Austell region. It has been found at Stennagwynn, with fluellite.

** For more on the career and publications of James Sowerby, including two fine handcoloured mineral catalogues, the 5-volume British Mineralogy and the 2-volume Exotic Mineralogy (1802-1820), see Conklin (1995).

Worldwide occurrence

A number of occurrences have been described (e.g., Moore, 2016, volume 2, pp.686-689, summarized below, with additional notes and references) for fine specimens on the market in the past five or six decades:

  • The Gunheath pit, Cornwall. A china clay pit, with wavellite in quartz-tourmaline greisen, associated with turquoise and other phosphates.
  • The High Down quarry near Barnstable (sic), Devon.
  • Hingston Down quarry, Gunnislake, Cornwall.
  • Pwlldu Beach, Gower peninsula, south Wales.
  • Other European localities in France, Germany, Ireland, Italy and Poland. Fine wavellite is also reported from Palazuelos de las Cuevas, Zamora, Spain, sometimes ornamented by minute crystals of turquoise (Moore, 1994).
  • Arkansas, notably in sandstone and shale host rocks,as radiating acicular crystals and spheroids, often pale green in colour (Smith, 1985). Fine specimens may be either green or blue (Wilson, 2014).
  • Other U.S. localities in California (Moore, 2017), Nevada (Jensen et al., 1995; Jensen and Leising, 2001), Pennsylvania (Gordon, 1922; Hoff, 1999), Tennessee and Utah.
  • Bolivia, notably the Siglo XX mine in Llallagua (see Bandy, 1944; Turneaure, 1960; Kelly and Turneaure, 1970).
  • Peechelba area, Victoria, Australia.

There are of course other localities, as in Virginia (Artz, 1938) and Colorado (Cobban et al., 1997; Carnein and Bartos, 2005). Back in Pennsylvania, beautiful lime-green wavellite has been collected from Lime Ridge, Snyder county (Fitzgerald and Bainbridge, 2015; Polityka, 2016). At the Silver Coin mine in Nevada, there are crandallite pseudomorphs after wavellite, as well as sprays of wavellite crystals on metavariscite (Adams et al., 2015: it is a long time since I've come across an article describing so many minerals that I had never heard of previously, must be 10 or more! - GCW).

References, in chronological order (n=37)

Varley,D (1849) Rudimentary Treatise on Mineralogy for the use of Beginners. John Weale, London, 164+vipp.

Greg,RP and Lettsom,WG (1858) Manual of the Mineralogy of Great Britain and Ireland. 483+xvi pp., reprint of 1977.

Collins,JH (1892) A Handbook to the Mineralogy of Cornwall and Devon. D. Bradford Barton Ltd, 108pp. plus addenda and plates, reprint of 2nd edition in 1969.

Heddle,MF (1901) The Mineralogy of Scotland. Volume I, lviii+148pp., plates 1-51, and Vol.II, viii+247pp., plates 52-103.

Gordon,SG (1922) The Mineralogy of Pennsylvania. Academy of Natural Sciences of Philadelphia Spec.Publ. 1, reprinted by Dover Publications, Inc., New York, 1959, 255pp.

Artz,LC (1938) Occurrence of wavellite, Giles county, Virginia. Amer.Mineral. 23, 664-665.

Bandy,MC (1944) Mineralogy of Llallagua, Bolivia. Tucson Gem and Mineral Society Spec.Pap. 1, 67+16pp., reprinted 1976.

Russell,A et al. (1948) Guide to Excursion A4, Devon and Cornwall (Mineralogical). IGC 18 Field Trip Guide A4, 18pp.

Turneaure,FS (1960) A comparative study of major ore deposits of central Bolivia. Part II. Econ.Geol. 55, 574-606.

Kingsbury,AWG (1964) Some minerals of special interest in south-west England. In `Present Views on Some Aspects of the Geology of Cornwall and Devon' (Hosking,KFG and Shrimpton,GJ editors), Roy.Geol.Soc.Cornwall, 330pp., 247-266.

Metz,R (1965) Gems and Minerals in Color. Hippocrene Books, New York, Engl. Trans. 1974, 255pp.

Kelly,WC and Turneaure,FS (1970) Mineralogy, paragenesis and geothermometry of the tin and tungsten deposits of the eastern Andes, Bolivia. Econ.Geol. 65, 609-680.

Pough,FH (1970) A Field Guide to Rocks and Minerals. Constable, London, 2nd edition, 349pp., 1960, republished in UK.

Hofmann,F and Karpinski,J (1981) Rare and Beautiful Minerals. Exeter Books, N.Y.C., Engl. transl. of Ger. original, 226pp.

Smith,AE (1985) Aluminum phosphate minerals from Mauldin Mountain, Montgomery county, Arkansas. Mineral.Record 16 no.4, 291-295.

Embrey,PG and Symes,RF (1987) Minerals of Cornwall and Devon. British Museum (Natural History) / Mineralogical Record Inc., 154pp.

Moore,T (1994) What's new in minerals? Tucson show 1994. Mineral. Record 25, 211-222.

Jensen,MC, Rota,JC and Foord,EE (1995) The Gold Quarry mine, Carlin-Trend, Eureka County, Nevada. Mineral.Record 26, 449-469.

Conklin,LH (1995) James Sowerby, his publications and collections. Mineral.Record 26 no.4, 85-105.

Kourimsky,J (1995) The Illustrated Encyclopedia of Minerals & Rocks. Adventinum Publishing House, Prague / Sunburst Books, London, Engl. edition, 256pp.

Pough,FH (1996) A Field Guide to Rocks and Minerals. Houghton Mifflin Company, Peterson Field Guides, 5th edition, 396pp.

Cobban,RR, Collins,DS, Foord,EE, Kile,DE, Modreski,PJ and Murphy,JA (1997) Minerals of Colorado by Edwin B. Eckel. Fulcrum Publishing, Golden, CO, 665+40pp.

Hoff,DT (1999) Minor resources. In `The Geology of Pennsylvania' (Shultz,CH editor), Pennsylvania Geological Survey / Pittsburgh Geological Society, Spec.Publ. 1, 888pp., 644-655.

Jensen,M and Leising,J (2001) Wavellite, fluellite and minyulite from the Willard mine, Pershing county, Nevada. Mineral.Record 32, 297-303.

Bonewitz,RL (2005) Smithsonian Rock and Gem. DK Publishing Inc. / Smithsonian Institution and Dorling Kindersley Limited, 360pp.

Carnein,CR and Bartos,PJ (2005) The Cripple Creek mining district. Mineral.Record 36, 143-185.

Thomas,A (2008) Gemstones: Properties, Identification and Use. New Holland Publishers (UK) Ltd, 256pp.

Thompson,SE (2011) Wavellite. Lapidary Journal & Jewelry Artist 64 no.11, 26-27, March.

Erickson,L (2011) How to solder jewellery, 10: wavellite pendant. Lapidary Journal and Jewelry Artist 65 no.7, 42-46, December.

Melgarejo,JC and Martin,RF (2011) Atlas of Non-Silicate Minerals in Thin Section. Canadian Mineralogist Spec.Publ. 7, 522pp. plus CD-ROM.

Wilson,WE (editor) (2014) Mineral Collections in Texas. Mineral.Record 45 no.5, supplement, 304pp., September.

Fitzgerald,S and Bainbridge,M (2015) The Collector and his Legacy: Irénée du Pont and the Mineralogical Collection of the University of Delaware. Mineral.Record 46 no.3, supplement, 84pp., May.

Adams,PM, Wise,WS and Kampf,AR (2015) The Silver Coin mine, Iron Point district, Humboldt county, Nevada. Mineral.Record 46, 701-728.

Polityka,J (organizer) (2016) Mineral Collections in the American Northeast. Mineral.Record 47 no.4, supplement, 460pp., July.

Moore,TP (2016) Moore's Compendium of Mineral Discoveries, 1960-2015. Mineralogical Record, Inc., Tucson, 2 volumes, 809+813pp.

Moore,TP (editor) (2017) Mineral Collections in California. Mineral.Record 48 no.4, supplement, 296pp., July.

Graham Wilson, 29 December 2017- 03 January 2018

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