SCHORL, in mineralogy, a species of the Flint genus, which is divided by %Ver ner into two sub-species, viz. the common schorl and the tourmaline. The common schorl is black. It occurs often massive and disseminated, seldom in rolled pie ces, and frequently cry stallzed The crystals are mostly acicirlar ; fragments, when broken, indeterminably angular ; it very rarely presents coarse and small grained distinct concretions ; sometimes it occurs in very thin, and but rarely in thick, straight and prismatic distinct con cretions. It is opaque, and but little trans lucent on the edges, when it passes to the tourmaline. It gives a grey streak ; is hard, and very easily frangible. Specific gravity from 3.09 to 3.21. It melts before the blow-pipe, without addition, into a blackish slag. Melted with borax,it forms a greenish-coloured glass. It is composed of Silica 33.33 Alumina - - - - 40.83 Iron 20,41 Manganese - . - - 3.33 97.90 Loss - - • 2.10 100 By heating, it exhibits positive electricity at one end, and negative at the other : as it cook, these electricities are reversed. It occurs in primitive rocks, chiefly in quartz and granite ; with the former, it constitutes a peculiar mountain rock. It is found on many parts of the continent, and in Scotland. It differs from tourma. line in colour degree of htstre, fracture, transparency, and distinct concretions; also in geognostic situations : tourmaline occurs almost always imbedded, and in single crystals; but schorl is aggregated, and occurs in beds.
Tourmaline, called also electricus tur malin, is of a green or brown colour, passing into others, even to the indigo blue. The colours are mostly dark. It occurs very seldom massive, oftener in rolled pieces, but most frequently crys tallized. The crystalsare generally three
sided prisms ; they are usually imbedded ; the internal lustre is splendent and vi treous. It is hard, and easily frangible. Specific gravity from 3 08 to 3.36. Before the blow-pipe it melts into a greyish white vesicular enamel. It was found in Ceylon and the Brazils, in the 16th cen tury ; and since that in Madagascar and Ava, in many parts of the European con tinent, and in Scotland. Two specimens have been analyzed by Bergmann and Vatiquelin, the former was brought from Ceylon, the latter from Brazil.
Tourmaline of Ceylon. Of Brazil. Silica - - - 37.0 - — 40.0 Alumina - - 39.0 . - 39.0 Lime - - - 15.0 - — 3 84 Oxide of iron 9.0 - - 12.50 — manganese - - - 2.00 100.0 97.34 Loss 2.66 100.00 Tourmaline has been long celebrated for its electrical effects, which are exhi bited by friction, and also by heating : but if it is made very hot, as beyond 200° of Fahrenheit, it is deprived of its electri cal properties. The more transparent the tourmaline, the stronger its electrical properties. II is sometimes cut and po lished, and worn as a jewel ; but on ac count of its want of transparency it is not very highly esteemed. The green co. loured tourmaline has been described as the emerald ; the blue, as the sapphire ; and the crimson-red variety, first found in Siberia, and since in Ava and Ceylon, has been called the daurite, siberite, and ru• be Hite. Mr. Greville is in possession of the most magnificent specimen of the red va. riety ; it is valued, on account of its beauty and rarity, at 10001.