Unusual Banded Barite from Barras End Mine,
Swaledale, North Yorkshire

Peter J. Briscoe

Dark brown barite, not dissimilar in colour to the famous oakstone of Derbyshire, occurs on a few small dumps at Barras End Mine in Swaledale, North Yorkshire. The barite, which is quite distinct from the typical white North Pennine material, was deposited at a late stage in open voids. Cavities within the massive banded barite are commonly lined with translucent brown prismatic crystals. In some cases these are overgrown by well crystallised hemimorphite. Strontianite, cinnabar and aurichalcite are present on a few specimens. Cut and polished sections commonly display attractive figuring.

Polished section through a coarsely crystallised brown barite mass 40 mm across. Photo Julie Ballard.

A double page spread from this article

Digital Combination Photography
of Micro-Minerals Using Bellows Lenses

David I. Green
Volker Betz

Software that combines the sharply focussed areas of a series of digital photos offers significant advantages when imaging specimens at magnifications greater than life-size. Traditionally, photographers have used two methods to attain high magnification: photography through the microscope or through specialised bellows lenses. This paper concentrates on the second technique, using bellows lenses. To get the best results it is important to understand the limitations of the lenses. In particular, their depth of field and resolution at different magnifications and apertures must be taken into account. If this is done properly, high quality images of micro-mineral specimens with an enormously enhanced depth of field can be produced.

Topaz crystals, the largest 9 mm in length from Topaz Mountain, Thomas Range, Utah. This specimen was photographed using a Zeiss Luminar 63 mm lens with minimal bellows extension. The image is a combination of six digital photos. It is about as large a reproduction ratio as is possible while maintaining real detail in the image. Multi-focus photo by David Green.

A double page spread from this article

Classic Nineteenth Century Fluorite Specimens from Weardale, Durham:
A Mineralogical Mystery

Jesse Fisher

Nineteenth century mineral specimens from the North Pennine Orefield in northern England are often only vaguely located. Where there is any data at all they are usually labelled simply as “Cumberland” or “Alston Moor”. Collectors and dealers commonly assume that all the old-time specimens of green fluorite from the orefield originated in the famous workings of Heights Mine near Westgate in Weardale. However there is good evidence that some specimens with a distinctive matrix and crystal morphology were found at the nearby Middlehope Shield Mine.

A cluster of twinned fluorite crystals, 10 cm across, with minor galena, possibly from the 1818 find at White’s Level on Middlehope Burn. Photo Jesse Fisher.

A Mineralogical Tour of the
Kingdom of Fife

Stephen Moreton

The Kingdom of Fife on the eastern coast of Scotland has a varied geology and has produced a considerable variety of mineral species many of which are the result of volcanic activity. The north Fife hills are particularly rich in agates. Pyrope and zircon are present in a volcanic vent near Elie. Hydrothermal activity associated with volcanism has produced quartz, calcite, dolomite and barite veins at several coastal localities. At Orrock Quarry, apophyllite, pectolite and prehnite are found in lavas. Some of the best pyrite crystals found in Scotland were collected at Goat Quarry in the 1990s and traces of copper and uranium mineralisation have been found in felsite at Balmullo Quarry.

Agates from Colluthie Hill near Luthrie collected by Stephen Moreton.

The First British Occurrence of Cesàrolite at Eaglebrook Mine,
Ceulanymaesmawr, Ceredigion, Wales

Tom F. Cotterell

The rare supergene manganese mineral cesàrolite has been identified on a specimen from Eaglebrook Mine, Ceredigion, Wales. It occurs as inconspicuous black botryoidal crusts in intimate association with gibbsite. The X-ray powder diffraction data is compared with new data for cesàrolite from the type locality and with published data. A small systematic shift in the d-spacings (compared to the published data) is attributed to improvements in instrumentation. This is the first record of cesàrolite in the British Isles and the first report of gibbsite in a supergene environment in Central Wales.

Acicular Wurtzite and Sphalerite from the
Lockridge Mine, Bere Alston, Devon

Ben A. Grguric
Ernest H. Nickel

The dumps of Lockridge Mine near Bere Alston in south Devon contain rich specimens of mixed zinc, lead and copper sulphides and sulphosalts overgrowing fluorite. Wurtzite-sphalerite intergrowths showing the ‘ice-fern’ texture, which is characteristic of wurtzite, are intergrown with silver-rich tetrahedrite, tennantite and galena. Close examination suggests that most of the zinc sulphide was deposited as wurtzite and then partially altered to sphalerite. A primary hypogene origin is suggested for all of the minerals described, with the excpetion of anglesite.

Copper minerals including the first Irish Clinoclase and Zálesíite
from Leaghillaun, Co. Kerry

Stephen Moreton
David I. Green

A small copper deposit discovered recently at Leaghillaun, Beara, Co. Kerry, is a member of a large group of similar stratabound base metal deposits that are hosted by the Devonian sandstones of southwest Ireland. The primary mineralisation is dominated by tennantite and chalcopyrite, which have oxidised to produce a suite of supergene minerals including azurite, malachite, cornwallite, chrysocolla and tyrolite. The uncommon copper arsenate clinoclase occurs as millimetre-size sheaves of dark blue-black plates and the rare calcium copper arsenate zálesíite as minute green acicular crystals. These appear to be the first reliable reports of the minerals in Ireland.

Fan-shaped aggregates of platy clinoclase crystals to 0.8 mm long. Stephen Moreton collection. Photo David Green.

The First British Occurrence of Arsendescloizite at
Sandbed Mine, Caldbeck Fells, Cumbria

Tim Neall
Andrew G. Tindle
David I. Green

The rare lead zinc arsenate arsendescloizite occurs as pale green crusts associated with calcium-rich mimetite at Sandbed Mine in the Caldbeck Fells, Cumbria. Quantitative chemical analyses show significant substitution of calcium for lead and of copper for zinc. They produce a chemical formula that can be written: (Na0.07,Pb0.71,Ca0.22)(Zn0.73,Cu0.27)[(AsO4)0.94,(PO4)0.04,(VO4)0.01)](OH)0.97, which is remarkably close to the ideal adelite-descloizite group formula. This is the first report of arsendescloizite in the British Isles.

Pale green crustose arsendescloizite on iron stained quartz with white calcium-rich mimetite from Sandbed Mine. Field of view is ca. 3 mm across. Tim Neall collection. Photo David Green.

The Composition of Tsumebite from Roughton Gill Mine,
Caldbeck Fells, Cumbria

Andrew G. Tindle
Trevor F. Bridges
David I. Green

There is extensive substitution of arsenate for phosphate in tsumebite from Roughton Gill Mine in the Caldbeck Fells, Cumbria. Calculated chemical formulae are in excellent agreement with the general brackebuschite group formula.The most arsenate-rich material has more than 50 atom% substitution in the phosphate site and can therefore be described as arsentsumebite. Arsentsumebite occurs as rims a few tens of micrometres thick, which surround tsumebite cores. This indicates an increasing arsenate activity as the mineral crystallised. Tsumebite is commonly found with well crystallised brochantite and is often associated with slightly corroded cerussite. This association provides an indication of the chemical conditions in which it formed, probably at pH of about 6 with a high sulphate ion activity.

Apple green spherules of tsumebite (to 1 mm) with arsenic-rich exteriors, associated with dark green brochantite and pyromorphite from Roughton Gill, Caldbeck Fells, Cumbria. Photo David Green.

Caryopilite and Pyroxmangite from
Nant Mine, Nant-Y-Gadwen, Llanfaelrhys, Pen Llyn, Gwynedd, Wales

Tom F. Cotterell

The rare manganese silicate minerals caryopilite and pyroxmangite occur in thin veinlets cutting siliceous manganese ore from Nant Mine, Nant-y-Gadwen, Llanfaelrhys, Pen Llyn, Gwynedd. Both occur as microcrystalline orange-brown veinlets in massive manganese ore. This is the first record of caryopilite in the British Isles and the first account of pyroxmangite in Wales.