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EPIDOTE , a See also:mineral See also:species consisting of basic See also:calcium, See also:aluminium and See also:iron orthosilicate, Ca2(A1OH)(A1,Fe)2(SiO4)3, crystallizing in the See also:monoclinic See also:system. Well-See also:developed crystals are of frequent occurrence: they are commonly prismatic in See also:habit, the direction of See also:elongation being perpendicular to the single See also:plane of symmetry. The faces lettered M, T and r in the figure are often deeply striated in the same direction: M is a direction of perfect cleavage, and T of imperfect cleavage: crystals are often twinned on the See also:face T. Many of the characters of the mineral vary with the amount of iron See also:present (Fe2O3,5-17%), for instance, the See also:colour, the See also:optical constants, and the specific gravity (3.3-3'5)• The hardness is 62. The colour is See also:green, See also:grey, See also:- BROWN
- BROWN, CHARLES BROCKDEN (1771-181o)
- BROWN, FORD MADOX (1821-1893)
- BROWN, FRANCIS (1849- )
- BROWN, GEORGE (1818-188o)
- BROWN, HENRY KIRKE (1814-1886)
- BROWN, JACOB (1775–1828)
- BROWN, JOHN (1715–1766)
- BROWN, JOHN (1722-1787)
- BROWN, JOHN (1735–1788)
- BROWN, JOHN (1784–1858)
- BROWN, JOHN (1800-1859)
- BROWN, JOHN (1810—1882)
- BROWN, JOHN GEORGE (1831— )
- BROWN, ROBERT (1773-1858)
- BROWN, SAMUEL MORISON (1817—1856)
- BROWN, SIR GEORGE (1790-1865)
- BROWN, SIR JOHN (1816-1896)
- BROWN, SIR WILLIAM, BART
- BROWN, THOMAS (1663-1704)
- BROWN, THOMAS (1778-1820)
- BROWN, THOMAS EDWARD (1830-1897)
- BROWN, WILLIAM LAURENCE (1755–1830)
brown or nearly See also:black, but usually a characteristic shade of yellowish-green or pistachio-green. The pleochroism is strong, the pleochroic See also:colours being usually green, yellow and brown. The names thallite (from OaXXos, " a See also:young shoot ") and pistacite (from 1rcvreucca, " pistachio See also:nut ") have reference to the colour. The name epidote is one of R. J. Haiiy's crystallographic names, and is derived from i rLSoves, "increase," because the See also:base of the See also:primitive See also:prism has one See also:side longer than the other. Several other names (achmatite, bucklandite, escherite, puschkinite, &c.) have been applied to this species. Withamite is a See also:carmine-red to See also:straw-yellow, strongly pleochroic variety from See also:Glencoe in See also:Scotland. Fouqueite and clinozoisite are See also:- WHITE
- WHITE, ANDREW DICKSON (1832– )
- WHITE, GILBERT (1720–1793)
- WHITE, HENRY KIRKE (1785-1806)
- WHITE, HUGH LAWSON (1773-1840)
- WHITE, JOSEPH BLANCO (1775-1841)
- WHITE, RICHARD GRANT (1822-1885)
- WHITE, ROBERT (1645-1704)
- WHITE, SIR GEORGE STUART (1835– )
- WHITE, SIR THOMAS (1492-1567)
- WHITE, SIR WILLIAM ARTHUR (1824--1891)
- WHITE, SIR WILLIAM HENRY (1845– )
- WHITE, THOMAS (1628-1698)
- WHITE, THOMAS (c. 1550-1624)
white or See also:pale See also:rose-red varieties containing very little iron, thus having the same chemical See also:composition as the orthorhombic mineral See also:zoisite (q.v.).
Epidote is an abundant See also:rock-forming mineral, but one of689
secondary origin. It occurs in crystalline limestones and schistose rocks of metamorphic origin; and is also a product of weathering of various minerals (felspars, micas, pyroxenes, amphiboles, garnets, &c.) composing igneous rocks. A rock composed of See also:quartz and epidote is known as See also:epidosite. Well-developed crystals are found at many localities, of which the following may be specially mentioned: Knappenwand, near the See also:Gross-Venediger in the Untersulzbachthal in See also:Salzburg, as magnificent, dark green crystals of See also:long prismatic habit in cavities in epidoteschist, with See also:asbestos, adularia, See also:calcite, and See also:apatite; the See also:Ala valley and Traversella in See also:Piedmont; See also:Arendal in See also:Norway (arendalite); Le Bourg d'Oisans in See also:Dauphine (oisanite and delphinite); Haddam in See also:Connecticut; See also:Prince of See also:Wales See also:Island in See also:Alaska, here as large, dark green, See also:tabular crystals with See also:copper ores in metamorphosed See also:limestone.
The perfectly transparent, dark green crystals from the Knappenwand and from See also:Brazil have occasionally been cut as See also:gem-stones.
Belonging to the same isomorphous See also:group with epidote are the species piedmontite and allanite, which may be described as See also:manganese and See also:cerium epidotes respectively.
Piedmontite has the composition Ca2(A10H)(Fe,Mn)2(SiO4)3; it occurs as small, reddish-black, monoclinic crystals in the manganese mines at See also:San See also:Marcel, near See also:Ivrea in Piedmont, and in crystalline See also:schists at several places in See also:Japan. The See also:purple colour of the See also:Egyptian porfido rosso antico is due to the presence of this mineral.
Allanite has the same See also:general See also:formula See also:R2"(R"'OH)R21"(SiO4)3, where R" represents calcium and ferrous iron, and R"' aluminium, ferric iron and metals of the cerium group. In See also:external See also:appearance it differs widely from epidote, being black or dark brown in colour, pitchy in lustre, and opaque in the See also:mass; further, there is little or no cleavage, and well-developed crystals are rarely met with. The crystallographic and optical characters are similar to those of epidote; the pleochroism is strong with reddish-, yellowish-, and greenish-brown colours. Although not a See also:common mineral, allanite is of fairly wide See also:distribution as a See also:primary See also:accessory constituent of many crystalline rocks, e.g. See also:gneiss, See also:granite, See also:syenite, See also:rhyolite, See also:andesite, &c. It was first found in the granite of See also:east See also:Greenland and described by See also:- THOMAS
- THOMAS (c. 1654-1720)
- THOMAS (d. 110o)
- THOMAS, ARTHUR GORING (1850-1892)
- THOMAS, CHARLES LOUIS AMBROISE (1811-1896)
- THOMAS, GEORGE (c. 1756-1802)
- THOMAS, GEORGE HENRY (1816-187o)
- THOMAS, ISAIAH (1749-1831)
- THOMAS, PIERRE (1634-1698)
- THOMAS, SIDNEY GILCHRIST (1850-1885)
- THOMAS, ST
- THOMAS, THEODORE (1835-1905)
- THOMAS, WILLIAM (d. 1554)
Thomas See also:Allan in 18o8, after whom the species was named. Allanite is a mineral readily altered by hydration, becoming optically isotropic and amorphous: for this See also:reason several varieties have been distinguished, and many different names applied. Orthite, from opOos, " straight," was the name given by J. J. See also:Berzelius in 1818 to a hydrated See also:form found as slender prismatic crystals, sometimes a See also:foot in length, at Finbo, near See also:Falun in See also:Sweden. (L. J.
End of Article: EPIDOTE
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