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 56 pages, full colour. |
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Digital Combination Photography:
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Left: It would be impossible to illustrate a blocky three
dimensional crystal such as this torbernite from Blackpool Pit,
St Austell, Cornwall using conventional photography. The crystal
is 1 mm across at it widest part and the total depth from front
to back is about 0.5 mm. The image was hand combined from 16 slices
each having a usable depth of field of about 30 µm. |
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A complex assemblage of minerals including arsenopyrite, cobaltite, chalcopyrite, scheelite, bismuth, erythrite, quartz, fluorite, stannite, bismuth, bismuthinite, aikinite, cosalite, gersdorffite, ikunolite and various bismuth-bearing supergene minerals is present on the dumps of the North Devon United Mine at Peter Tavy, Devon. The rare nickel bismuth sulphide parkerite (ideally Ni3Bi2S2) has been identified as grains up to 50 µm across in quartz-fluorite veinstone associated with sphalerite, ullmannite, bismuth, bismite, gersdorffite, an unknown lead copper sulphide selenide and cassiterite. Quantitative analyses of the parkerite record significant substitution of antimony for bismuth and include the most highly antimonian composition yet described, with 5.3 wt% Sb. This is the first report of parkerite in the British Isles.
The rare mineral ewaldite has been identified in mineralised tension
fractures in Precambrian sedimentary rocks of the Yat Wood Formation at
Dolyhir Quarry, Old Radnor, Powys. It crystallises as isolated pale yellow-brown
translucent striated hexagonal pyramids in association with harmotome,
witherite, calcite and quartz. This is the first record of ewaldite in
the British Isles.
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Left: A yellow-brown hexagonal crystal of the rare-earth
carbonate mineral ewaldite 2.5 mm long with colourless harmotome
from Dolyhir Quarry, Old Radnor, Wales. Photo David Green |
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Drusy cavities in the granite at Lindsay’s Leap in the Mourne Mountains,
Co. Down, contain a variety of minerals. They are lined with quartz and
feldspar and commonly contain mica and chlorite group species. Beryl,
calcite, chabazite-Ca, fluorite, heulandite-Ca, monazite-(Ce), saponite,
stilbite-Ca and topaz have also been identified, together with the first
Irish occurrence of the rare iron beryllium silicate sulphide danalite.
Danalite occurs rarely as small translucent brown crystals and grains
on joint planes and in small cavities with quartz, saponite and stilbite-Ca.
It is later in the paragenesis than all of the other silicate species
except the low temperature zeolite group minerals.
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Left: A single pale blue beryl crystal 5 mm long with
darker blue ghosts near its centre. Photo David Green. |
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The compositions of the magnesium and iron borate minerals boracite,
trembathite and congolite, which occur in Zechstein evaporites at Boulby
Mine, Redcar and Cleveland are described. Brown blocky crystals which
have been described in the literature as either iron-boracite or ericaite,
are in fact the recently described mineral trembathite, or the rare iron
borate congolite, or mixtures of both trembathite and congolite.
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Left: Bright blue pseudotetrahedral boracite crystals
to 3 mm from the 281 panel area, Boulby Mine. |
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The rare lead selenate sulphate mineral olsacherite has been identified on a single minute specimen collected at Waterbank Mine, Ecton, Staffordshire. It was present as an inconspicuous pale brown spheroidal crystal aggregate composed of sharp bladed crystals up to about 0.1 mm in length. A copper and selenium-bearing supergene mineral was identified on the same specimen. The ore deposits at Waterbank Mine appear to contain more selenium than hitherto suspected. This is the first report of olsacherite at any locality in the British Isles
SEM photo showing bladed crystals of olsacherite up to 0.1 mm across
from Waterbank Mine, Ecton Staffordshire.
Specimen collected by Steve Rust, photo David Green
The supergene mineralisation at Greystone Quarry near Launceston, Cornwall is unusually diverse. It includes eighteen lead-bearing supergene minerals, four which were new to Cornwall when first reported and one which was new to Britain. The rare supergene lead copper sulphate hydroxide elyite has recently been identified, adding another rare species to an already remarkable list. Elyite occurs as minute pale violet to purple sprays of acicular crystals which appear to have formed by natural supergene oxidation. This is the first report of elyite in Cornwall.
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Left: This image is a manually combined composite of
two separate slices. It shows radiating aggregates of purple elyite
on oxidised galena-chalcopyrite matrix. Richard De Nul collection
and photo. |
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The rare supergene mineral philipsbornite has been identified at Wheal Unity, Gwennap, Cornwall. It occurs in drusy crusts composed of minute trigonal crystals. Empirical formulae determined for two typical grains are in good agreement with theoretical expectations for members of the crandallite group. Iron, sulphate, phosphate and fluoride are the major chemical substitutions.
An SEM photo showing sharp trigonal philipsbornite crystals up to 0.05
mm long from Wheal Unity, Gwennap, Cornwall.
Chris Jewson collection.
lvaite, a rare calcium-iron silicate, is present in the dolerite-pegmatite facies of the Whin Sill at Forcegarth Quarry near High Force in Teesdale, Co. Durham. It has a near stoichiometric composition in the range Ca0.98-1.00Fe2+1.95-2.00Fe3+Si1.96-1.98O8(OH). Ilvaite forms part of an association of opaque minerals that includes ilmenite, altered titanomagnetite, titanite and minor sulphides, notably pyrrhotite, chalcopyrite and sphalerite that is characteristic of ilvaite in mafic igneous rocks. Other than the presence of ilvaite and trace amounts of molybdenite there is nothing unusual about the sampled dolerite-pegmatite suggesting that ilvaite may be present in dolerite-pegmatites elsewhere in the Whin Sill. This is the first authenticated occurrence of ilvaite in the British Isles.
The opaque mineralogy of pink aplite from the Whin Sill at Ratcheugh Quarry near Alnwick comprises ilmenite, titanite and pyrite with minor amounts of pyrrhotite, chalcopyrite, iron-rich sphalerite and galena. Much of the sulphide assemblage and associated barite is later than the crystallisation of the aplite.
FLUORSPAR IN THE NORTH PENNINES
edited by Raymond A. Fairbairn (2003)
Rob Ixer
FOSSICKING FOR MINERALS AT THE PUTTAPA
ZINC MINE, SOUTH AUSTRALIA
by Patrick and James Murphy (2000)
David Green
