New English Fluorite Update 18 March 2022

18 March 2022

FOLLOWING Tuesday’s update of British minerals, today we narrow the focus, concentrating on English Fluorite.

Fluorite is a remarkably common species throughout the world, yet every country appears to impart its own characteristic imprint, with a specimen’s unique traits instantly advertising its place of origin. The same is true for Fluorite within a country and English Fluorites exemplify this perfectly. Today’s selection is taken from across six counties, Cumbria, Derbyshire, Durham and Northumberland in the north and Cornwall and Devon in the far southwest.

In the eyes of worldwide collectors, without doubt the most well-known and recognisable English Fluorites are those from the Weardale valley in County Durham. For many centuries Fluorite was essentially just a gangue mineral in the lead and zinc mines of the region. Mention Weardale today and most of us picture vibrant green Fluorite yet, strangely, this colour seems not to have been encountered until a pocket was found in Middlehope Shield mine at Westgate in 1818, where it was initially thought to be Emerald!

Anyone who has collected in Derbyshire knows the South Pennine Orefield is fluorine-rich, making specimens of principally colourless Fluorite almost ubiquitous, although far from all are great specimens! The exception to the colourless rule is the area around the beautiful village of Castleton, world-famous for the blue variety of Fluorite known as Blue John. These Fluorite veins were worked by the Romans and ornaments such as Blue John vases, goblets and jewellery have been found in archaeological sites throughout the former Roman Empire.

Whereas Derbyshire mineralisation is rich in fluorine, the opposite can be said for Devon and Cornwall. One would think, given the mineral wealth of these two counties, good Fluorite specimens would be plentiful, yet this is not the case; the Cornubian Batholith was relatively devoid in fluoride with which to form Fluorite (fluoride being the mobile form of violently reactive fluorine). But all rules are made to be broken and where Fluorite did crystallise in Cornwall and Devon, my word, did it produce some beautiful specimens.

Just over half of today’s specimens are from Weardale, taking in both old and new mining localities. The largest is a magnificent Frazer’s Hush specimen covered in 1 cm cubic Fluorite crystals of characteristic lilac. It is wonderful in artificial light, but having just looked at it outdoors its natural daylight fluorescence is mind blowing! Another older Weardale piece is a fine Rogerley green Fluorite mined by Lindsay Greenbank and formerly in his collection. More recent finds include vivid green Fluorites from the Naughty Gnome, Truffle Pig, Hidden Forest and Milky Way Pockets in Diana Maria mine by Frosterley. From Lady Annabella mine at Eastgate, two gorgeous specimens from The Layer Cake Pocket and The Bull Vein, the latter a stunning colour zoned lemon yellow Fluorite which is breath-takingly gemmy! Also keep a look-out for the terrific smoky teal blue specimen with Siderite from Boltsburn West mine at Rookhope and a stunning large cabinet West Pastures specimen with wonderful apple green cubes.

Another stunning large cabinet specimen is a characteristic bed of colourless to pale lavender Fluorite crystals from the Diana Vein at Beaumont mine in East Allendale, Northumberland. This Diana Vein has no connection with the Diana Maria mine! The crystals can measure to almost 2 cm and often adopt a pale vanilla yellow hue which contrasts beautifully against a pervasive underlying bed of crystallised black Sphalerite.

Our two offerings from Cumbria are a golden-yellow miniature Fluorite from Hilton mine in Scordale and an intensely deep sky-blue Fluorite on white ‘pearl-spar’ Dolomite from Florence mine by the town of Egremont. Two wildly different and amazingly coloured Fluorites from the extreme east and west of Cumbria.

Two Derbyshire Fluorites represent both the colourless and blue verities already discussed. From Ladywash mine at Eyam, intergrown colourless Fluorite crystals tinged smoky yellow and measuring to 2.4 cm richly adorn a matrix of massive cryptocrystalline Fluorite. The Fluorite crystals reveal two separate phases of iron sulphide inclusions; one a deeper zone containing pale yellow-white metallic micro-crystals of bladed Marcasite and a near-surface zone containing micro-crystals of Pyrite. The large miniature of white cockscomb Baryte on deep purple cubic Fluorite is from the Castleton area. The Baryte has a light dusting of micro-crystals of Pyrite and is ex. The University of Halle, Germany and comes with a lovely and very neatly written detailed description in German (see photo).

We end with Devon and Cornwall. From Lockridge mine near Bere Ferrers in Devon, intergrown cubes of delicate pale blue-green Fluorite cover a matrix of massive Fluorite. The cubic crystals, to 1.4 cm, have beautiful pale cornflower-blue colour zoning close to, and parallel with, the crystal faces. From Wheal Mary Ann at Menheniot, a large miniature of citrus-apple-green cubic Fluorite crystals embedded in a druse of glassy Quartz crystals and a large miniature Fluorite with Calcite and Pyrite of delicate pastel lemon with an outer coating of equally delicate sky blue Fluorite. Lastly, from St. Agnes on the north Cornish coast, a gemmy-translucent, pastel blue Fluorite whose stepped edges, outlined in lilac, form a blocky pyramid of about 2.5 cm tall.

The ExtraLapis Fluorite book was subtitled The Collector’s Choice and indeed it is. Fluorite is probably the most widely collected of any mineral species, primarily for its seemingly infinite variations in colour, habit, associations and localities, not to mention aesthetics. So enjoy poring over today’s English Fluorites with the aim of finding one on which to get your paws on! PT

Here is what you have to look forward to in next week's update:

Tuesday 22nd & Friday 25th March - Europe

                                         

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Author: JH
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