Mineral Specimen Fakes and Forgeries

Don Edwards

Whenever and wherever collectible objects change hands for substantial (and sometimes even modest) sums of money there is a temptation to produce an item of value from materials of lower or even inconsequential value, creating a fake or forgery. This temptation is perhaps not as prevalent in mineralogy as it is in antiques or fine art, but it does exist. A few examples of mineral fakes and forgeries from across the world are given below. Collectors and dealers need to be aware of the various fakes and forgeries which are on the market and should examine new specimen discoveries with a critical eye.

A specimen of wire silver grown by in a home laboratory. Note the blackened silver sulphide bottom of the specimen and the absence of convincing matrix and associations. Photo: Don Edwards

The Rogerley Mine, Weardale,
County Durham, England

Jesse Fisher
Lindsay Greenbank

The mining districts of northern England have long been famous for fine mineral specimens. These include remarkable fluorite crystals, which are highly fluorescent and deeply coloured. Of all the coloured fluorites, green crystals are perhaps the most highly prized. The Rogerley Mine in Weardale has produced exceptionally fine specimens of green fluorite for the last three decades. It is currently operated as a specimen mine by UK Mining Ventures, a company owned by a group of American collectors and mineral dealers. The mineralogy of the deposit is relatively simple, comprising major primary fluorite and galena in clay filled cavities in metasomatic replacement flats and veins. Analyses of the trace element composition of coloured fluorite from the Rogerley Mine shows no obvious correspondence between colour and REE content. Thus rare earth elements are probably not the primary chromaphores in the fluorite.

Glassy green fluorite twins with slightly rough pitted crystal edges, collected 2002. Photo: David Green	Deep inky-purple fluorite twins, up to 25 mm on edge, with drusy white quartz. Collected in 1987 by David Green and Jean Spence from the Sutcliffe vein at Rogerley Quarry. Photo: Julie Ballard.

The Distribution of Rare Earth Elements in North Pennine Fluorspar and Fluorite

Rob Ixer

Fluorite ore (fluorspar) from the North Pennines is both colourful and rare earth element-rich and it has long been suggested that rare earth elements (REE) held within the lattice of fluorite are responsible for the range of colours seen in the mineral. Although a number of fluorspar and fluorite samples have been analysed to discover any relationship between rare earth content and colour there is still no consensus. Part of the problem has been inappropriate sampling. Detailed mineralogy and petrography of paragenetically early fluorspar show it to carry discrete REE minerals including phosphates (monazite and xenotime) and fluorocarbonates (mainly synchysite). Similarly early fluorite carries synchysite inclusions. By contrast, later generations of fluorspar, as exemplified by material from Rogerley Mine, are free of discrete REE minerals so that fluorite in those ores becomes the most significant REE-bearing phase. Any future rare earth element analyses of North Pennine fluorite should be undertaken after petrographical and paragenetic studies of that fluorite and its associated fluorspar ore in order to establish the presence or absence of any other REE-bearing phases.

The Barite and Supposed Celestine from the Triassic Mudstone
of Sidmouth, Devon

Keith Corrie
David Green

A large cliff fall from the west side of Peak Hill, Sidmouth, Devon has recently revealed remarkable pale blue to honey brown barite crystals in cavities in calcite nodules. These are from the same locality as specimens reported from Sidmouth in the late-nineteenth century, which were described erroneously as celestine. The barite is restricted to a few distinct nodule bands in red and green mudstone rocks of Middle Triassic Ladinian Age, which form the Sidmouth Mudstone Formation. The crystals, which reach up to 70 mm in length, are usually tabular on the c-axis and commonly elongated along the a-axis. They are strongly fluorescent and phosphorescent. Barite crystallisation appears to have taken place at a late-stage in the diagenesis of the mudstone, after the calcite nodules formed, by slow diffusion into the cavities through a restricted series of fractures.

A honey-brown barite crystal, highly elongated on the a-axis, on drusy calcite. Collected from the cliffs below Peak Hill, Sidmouth, Devon, in 2000 by Keith Corrie and donated to the Manchester Museum. Photo: David Green.

A group of platy golden brown barite crystals 22 mm long on drusy calcite. Peter Briscoe collection. Photo: Julie Ballard.

A sketch from the Diary of Peter Orlando Hutchinson showing the position of the celestite band in the cliffs below Peak Hill. It is perhaps worth noting as an aside, that Victorian geologists had something of an obsession with bands and beds, especially as far as fossils are concerned. Later work has shown that the fossil bands identified in this area were largely figments of the imagination (Dineley and Metcalf, 1999), but barite certainly does occur in distinct bands. Reproduced from diaries held by the Devon Record Office, Exeter, reference Z19/36/16d.

Copper Minerals from
Flamborough Head, East Yorkshire

Peter Roydhouse
David Green

Copper minerals occur in beach pebbles derived from the chalk of Speeton Cliff, near Flamborough Head. Millimetre-size cores composed of copper and cuprite and surrounded by alteration haloes of pale green malachite and an unidentified copper chloride mineral. Minor azurite is also present. This appears to be the first report of copper mineralisation from the chalk of the Yorkshire coast.

The Occurrence of Bechererite
in the British Isles

Steve Rust
Richard Bell
David Green

Bechererite is an exceptionally rare zinc copper sulphate silicate that forms as a result of the post-mining oxidation of copper and zinc sulphides in mine spoil. It has been identified on specimens collected at five mines in the Central Wales Orefield in the counties of Ceredigion and Powys and at one mine in the Caldbeck Fells, Cumbria. Bechererite typically occurs as minute, colourless, pale blue and pale green inverted pyramidal and cone-shaped crystals terminated by bright pedion faces. These appear to be characteristic of the species and are not readily confused with any other mineral found in post-mining assemblages except susannite.

Cone shaped bechererite crystals with flat pedion terminations from Frongoch Mine, Ceredigion. The photo clearly shows the hemimorphic crystal habit which is characteristic of the mineral. Mike Rothwell specimen and photo.

Bechererite crystals to 0.2 mm with trigonal pedion terminations and steep pyramidal faces. Specimen from Driggith Mine, Caldbeck Fells, Cumbria in the Richard Bell collection, SEM photo by Mike Rothwell

Chalcophanite from Drosgol Mine, Ponterwyd, Ceredigion:
The First Welsh Occurrence

Tom Cotterell
John Mason

A remarkable occurrence of the rare zinc iron manganese mineral chalcophanite is reported from Drosgol Mine in the Central Wales Orefield. Chalcophanite forms dark grey to black masses in veins in bleached, pinkish brecciated mudstone of Ashgill Age, exposed at a high level on the Camdwr Lode, where it cuts across the flank of Drosgol Hill. The mineralisation is interpreted as a highly oxidised supergene remnant of original hypogene mineralisation, with manganese supplied by wallrock leaching and zinc by the oxidation of sphalerite.

An SEM image showing well formed platy chalcophanite crystals to 0.4 mm on manganiferous matrix. Tom Cotterell specimen and photo.

The Use of a Portable XRF Within an Early Nineteenth Century Cobalt Mine on
Alderley Edge, Cheshire

Simon Timberlake
Stephen Mills

In July 1997 a portable XRF analyzer was field tested underground within the workings of the mine known as the ‘Cobalt Mine’ located beneath The Wizard Inn and the National Trust car park on Alderley Edge. This fieldwork was carried out in an attempt to assay in situ the cobalt, nickel and vanadium content of a cobalt-bearing wad (asbolane) present as coatings in fault cavities and as segregations within the sandstone wall-rock. Analyses show that the cobalt, vanadium and nickel content of the ore is extremely variable, but bulk ore had a low cobalt content. The technique is useful as a rapid means of determining the approximate grade of ores where there is no other obvious characteristic to rely on.

A contemporary painting of cobalt ore from Alderley Edge, Cheshire.

“On the estate of Sir John Thomas Stanley, Bart., at Alderney Edge in Cheshire, was found this variety and mixture of Cobalt. The substance being now so very scarce and valuable, the knowledge of this variety is of the more consequence, as it may lead to the finding of this Mineral on some unexpected occasions. The bloom of Cobalt having the crimson cast, is apt to betray it, and I hope, for the owner’s sake, this may become more profitable than hitherto, and lead to the acquisition of the more perfect substance. This is so mixed with Sand, Oxide of Copper, Manganese, &c., that it is of but little value as an Ore of Cobalt.”

Reproduced from Sowerby (1811).

REVIEWS

Minerals of Scotland
by Alec Livingstone (2002)
David Green

MDAT-COLL TITEL 03
by F. & G. Pfeiffer (2002)
David Green