Corsi Collection of Decorative Stones

Class II
Fluorspars (Spato fluore)

This fossil also known under the names of vitreous spar and fossil spar, is only a fluorate of lime. It often accompanies metallic ores. Hill 83 observed that [p133] lead gives it a yellow colour and cubical form; iron renders it red and rhomboidal or octahedral; tin renders it black and violet or amethyst colour, and of a quadrilateral shape; manganese gives it a purple or delicate violet colour; copper renders it dark blue or greenish. When spar is heated by fire it becomes crackled. It takes a superb polish, but is difficult to work because it is so friable. The most beautiful specimens are found in Darbishire in England.

See note in 'Section VI Argillaceous Stones' for the term 'fossil'. Another example of the use of this term is by Georgiana, Duchess of Devonshire (1757-1806), the mother of the 6th Duke of Devonshire, who formed a fine collection of so-called 'fossils'; mainly mineral specimens.

Although trace metals are responsible for colouration in a lot of minerals, the wide variety of colours in fluorite are caused by a number of agents including traces of rare elements not known in Corsi's time, sub-atomic level flaws in the crystal lattice, and natural radioactivity.


538. (133.1) Spato di Siena. White ground with long crystals and sardonyx coloured veins. (Rare).

539. (133.2) Spato di Darbishire. Yellow ground with sulphate of baryte and a great deal of lead, found at Chrich. (Very rare).

'Chrich' is an old spelling of Crich, Derbyshire. In the 19th century, fluorspar (the commercial term for the mineral fluorite) was a waste product of lead mining, but now has greater economic value as a flux for smelting metals (for which reason it got its name from the Latin fluere, meaning 'to flow') and as a raw material for chemical industries.

Nos. 539-543 were given to Corsi by the 6th Duke of Devonshire.

540. (133.3) Another from the same place. Ground of light amethyst colour, with some darker veins. (Rare).

541. (133.4) Another from the same place, formed of [p134] long purplish, whitish, and strong yellow stripes, found in Castelton. (Very rare).

This is a block of the variety of fluorite known as Blue John, which was obtained uniquely from extensive caverns and mines in Treak Cliff hill at Castleton (spelt by Corsi in the Italian manner) in Derbyshire. This special form of fluorite, notable for its deep colouring and attractive banding, was very widely popular in the 18th and 19th centuries for turning to make ormolu and other objets d'art. A full account of this stone, with illustrations, is given by Ford i (2000).

Usually when Corsi indicates 'from the same place' it has been taken to mean just that. In this instance, he means 'from Derbyshire'; Castleton is some 30 km from Crich.

i. Ford (2000)

542. (134.5) Another from the same place a mixture of transparent yellow, and white, found at Chrich. (Very rare).

543. (134.6) Another from the same place, called bleu Giovanni. It is of a deep purplish colour and found uniquely at Castelton. (Very rare).

Corsi, curiously, translates part of the name 'Blue John' into French, and the other part into Italian. It is perhaps worth noting that one possible derivation of the name 'Blue John' is the French 'bleu-jaune' because the banding is often purple-blue and yellow, but with no obvious French associations with this stone, the origins of the name remain obscure. Unlike nos. 540 and 541, this sample is cut parallel to the banding, which is clearly visible on the sides of the specimen.