Online Encyclopedia


Online Encyclopedia
Originally appearing in Volume V16, Page 464 of the 1911 Encyclopedia Britannica.
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LEPIDOLITE, or LITHIA-MICA, a mineral of the mica group (see Mica). It is a basic aluminium, potassium and lithium fluo-silicate, with the approximate formula KLi [Al(OH,F)2] Al(SiO3)3. Lithia and fluorine are each present to the extent of about 5%; rubidium and caesium are sometimes present in small amounts. Distinctly developed monoclinic crystals or cleavage sheets of large size are of rare occurrence, the mineral being usually found as scaly aggregates, and on this account was named lepidolite (from Gr. XE7ric, scale) by M. H. Klaproth in 1792. It is usually of a lilac or peach-blossom colour, but is sometimes greyish-white, and has a pearly lustre on the cleavage surfaces. The hardness is 21-4 and the sp. gr. 2.8-2.9, the optic axial angle measures 500-700. It is found in pegmatite-veins, often in association with pink tourmaline (rubellite) and some-times intergrown in parallel position with muscovite. Scaly masses of considerable extent are found at Rozena near Bystrzitz in Moravia and at Pala in San Diego county, California. The material from Rozena has been known since 1791, and has some-times been cut and polished for ornamental purposes: it has a pretty colour and spangled appearance and takes a good polish, but is rather soft. At Pala it has been extensively mined for the preparation of lithium and rubidium salts. Other localities for the mineral are the island of UtS in Sweden, and Auburn and Paris in Maine, U.S.A.; at Alabashka near Mursinka in the Urals large isolated crystals have been found, and from Central Australia transparent cleavage sheets of a fine lilac colour are known. The lithium-iron mica zinnwaldite or lithionite is closely allied to lepidolite, differing from it in containing some ferrous iron in addition to the constituents mentioned above. It occurs as greyish silvery scales with hexagonal outlines in the tin-bearing granites of Zinnwald in the Erzgebirge, Bohemia and of Cornwall. (L. J. S.)
End of Article: LEPIDOLITE
LEPIDOPTERA (Gr. ?emir, a scale or husk, and 7rrepo...

Additional information and Comments

LEPIDOLITE. Experiments with Lepid from Cligga mine St Agnes Cornwall UK has been observed that Lepido is Thermochromic, the experiment was performed with 10 g of the rough (as found) massive Lepido, this occurs in the dumps of the old mine. 10 g was crushed fine to pass 250um siev and dried at 110 C for 2 hours, here it was found that the pink lavender Lipido had lost the bright colour to give a grey colour, upon cooling overnight the original colour returned. It is also possible that Lepido is photo sensitive due to the observation showing a remaining grey colour under the surface colour,after heating heating under a heat lamp there was no pink lavender colour but under the surface was the original colour, within a day or so the full colour returned fully. Further experiments are ongoing once sufficient material has been collected from the same sorce. David
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