New British Update 15 March 2022

15 March 2022

THIS week we return to British minerals, a mixed selection today and then English Fluorite on Friday. The Fluorite picks are from all across England, showcasing the variety of colours and habits found.

Today is all about mineral diversity, with Cornwall grabbing the lion’s share with 12 specimens. This is followed by Cumbria with four and then Derbyshire with two and Devon with one. The remaining specimens are from two counties we seldom include in these updates, Cheshire and Staffordshire, so let’s begin our overview by looking at these localities in a little more detail.

The Alderley Edge copper mines in north Cheshire, just 19 km (12 miles) south of Manchester, date back to the Bronze Age and were worked intermittently up until the 1920s. Most of the mines are owned by the National Trust and access is still possible through the Derbyshire Caving Club. Although Cheshire is a relatively flat county, the shallow Alderley mines lie under a densely wooded sandstone escarpment which rises about 110 m (360 ft) above the Cheshire plain. The permeable nature of the sandstone allows the mines to drain and remain, on the whole, dry, so sill allowing almost full access. Alderley Edge does not produce spectacular mineral specimens, but 46 species are recorded and its mineralisation is instantly recognisable. The cabinet specimen we offer is from Engine Vein mine, displaying characteristic, interstitial pore-hosted Malachite-Azurite-Cerussite mineralisation within a sandstone-rich conglomerate. Alderley Edge is a faulted horst of Triassic sandstones, conglomerates and marls. Natural dynamic pumping drove metal-rich brines from the Irish Sea basin and surrounding sedimentary rocks, causing them to pond and then precipitate minerals in the crest of the horst, resulting in the ore deposit we observe today.

The county of Staffordshire shares borders with both Cheshire and Derbyshire and the Ecton mines in east Staffordshire lie in the western extremity of the South Pennine Orefield, within which almost all of Derbyshire’s minerals and mines are associated. The Ecton mines are part of the Peak District National Park but differ from Derbyshire’s lead and zinc mines in that they produced copper. The rich cabinet specimen we offer today from Ecton mine (Deep Ecton Pipe) displays intergrown metallic golden Chalcopyrite crystals richly covering botryoidal, white cockscomb Barite. Mining here also goes back to the Bronze Age, eventually ending in the 1890s. Underground visits are still conducted by the Ecton Hill Field Studies Association.

Venturing into Derbyshire we have an attractive Aurichalcite with Hemimorphite and Baryte from the Western Flats on the 60 fm Level at Golconda mine near Hopton and a Phosgenite on Galena from its type locality in Bage mine at Cromford. When first discovered, Phosgenite was initially named Cromfordite. I can’t say this is a particularly aesthetic specimen, but this miniature does display a glassy block of Phosgenite to 1.3 cm from this most sought after locality.

From Devon in the south west of England we have something rather unusual, a Linarite collected by Richard Barstow in March 1980, from Furzehill mine near to Bere Alston, north of Plymouth. Linarite is a mineral very rarely encountered in these mines. On this specimen, micro-crystallised patches of light azure blue Linarite form over the surfaces of a granite matrix together with minor Fluorite, Quartz, Chalcopyrite and Cerussite. Discerning collector Dick Barstow must have valued this as a rare, if not unique location piece, to incorporate it in his collection and is therefore accompanied with one of his white labels.

Over half of today’s update is from Cornwall, so a quick run through is essential reading! We were trying to avoid Fluorite today, given this Friday’s bumper update, but succumbed to a beautiful Chalcopyrite with Fluorite on Siderite from Carn Brea mine at Illogan, between Camborne and Redruth. Intense deep purple Fluorite forms cubic crystals to 1 cm with lustrous brassy, tetragonal Chalcopyrite crystals, both sitting on a bed of milk chocolate-brown Siderite blades.

Other Cornish delights include Carbonate-rich Fluorapatite (formerly Francolite) from Fowey Consols, Tywardreath; Cassiterite from Balleswidden mine at St. Just and Dolcoath east of Camborne. We have a Varlamoffite collected from the old dumps at Cligga mine, St. Agnes, by Sir Arthur Russell in July 1951 and a rather superb Pseudomalachite with Quartz, certainly from Cornwall and probably from the Old Gunnislake mine at Calstock.

We must also mention a lovely Bismuthinite from Fowey Consols; an excellent miniature crystalised Sphalerite from St. Agnes; octahedral Cuprite from Wheal Gorland; a magnificent Quartz from Wheal Jane; Chalcopyrite with Specular Hematite on Siderite from Tincroft mine, Illogan and fascinating hexagonal prisms of Calcite from 19 Level Load Drive, Geevor mine, with milky-white pinacoidal terminations.

This just leaves Cumbria of which we have two Scheelite specimens from Carrock mine, a once favourite site with UK collectors prior to a total ban being imposed by the local authorities. Carrock mine produced tungsten and was the only such British deposit outside of south west England. One of our two specimens occurs with Wolframite and in both, the octagonal Scheelite crystals fluoresce pale, ethereal bluish white under SWUV. The Scheelite with Wolframite is accompanied with a Department of Mineralogy, British Museum (Natural History) label and a hand written Bryce M. Wright label dated 1867.

Finally we have an elegant and rather impressive glassy Aragonite and powder blue tabular Baryte crystals, both from the Frizington mining district of west Cumbria.

We know British minerals are popular, so we do hope you find this selection interesting and wide-ranging, giving a snapshot of various types of ore deposits around the country. You can investigate each specimen in more detail via the hyperlinks to ensure it is that essential piece you require. Enjoy. PT

                                         

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Author: JH
Categories: Updates

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