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REALGAR

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Originally appearing in Volume V22, Page 941 of the 1911 Encyclopedia Britannica.
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REALGAR , a See also:

mineral See also:species consisting of See also:arsenic mono-sulphide (See also:AsS) and occurring as See also:monoclinic crystals of a See also:bright red See also:colour. There is a perfect cleavage parallel to the See also:plane of symmetry (r in fig.). The lustre is resinous, and the streak has the same colour as • the crystals, namely, See also:orange-red to See also:aurora-red. The hardness is I2–2 and the specific gravity 3'55. On exposure to See also:light the crystals crumble to a yellow See also:powder. The name realgar is of Arabic origin, and was used by the alchemists; the substance was known to See also:Theophrastus under the name EavbaplKrt, and to See also:Pliny as Sandaracha. The mineral usually occurs in association with the yellow arsenic sulphide, See also:orpiment. See also:Good crystals are found with ores of See also:silver and See also:lead in the mineral See also:veins of Felsobanya, near Nagy-Banya, Kapnik-Banya and Nagyag, near See also:Deva, in See also:Hungary; with See also:blende in the See also:white crystalline See also:dolomite of the Binnenthal in See also:Switzerland; and in a See also:bed of sandy See also:clay at Mercur in See also:Utah. It is deposited by the solfataras near See also:Naples and by the hot springs of the Yellowstone See also:National See also:Park. Realgar has been used as a pigment and in pyrotechny for producing a brilliant white See also:fire; but it is now replaced by the artificially prepared See also:compound. The other native arsenic sulphide, As2S3, known as orpiment (See also:Lat. auripigmentum, meaning " See also:golden paint " ), occurs as foliated masses of a See also:lemon-yellow colour, the foliation being parallel to a direction of perfect cleavage. It is sectile and soft (H.=12 2), and has a specific gravity 3.4.

Distinctly See also:

developed crystals are rare; they have usually been considered to be orthorhombic and isomorphous with See also:stibnite (Sb2S3), but it is probable that they are really monoclinic. Orpiment is extensively See also:mined near Julamerk in See also:Asiatic See also:Turkey. (L. J.

End of Article: REALGAR

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