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CORUNDUM , a See also:mineral composed of native alumina (Al203), remarkable for its hardness, and forming in its finer varieties a valuable See also:gem-See also:- STONE
- STONE (0. Eng. shin; the word is common to Teutonic languages, cf. Ger. Stein, Du. steen, Dan. and Swed. sten; the root is also seen in Gr. aria, pebble)
- STONE, CHARLES POMEROY (1824-1887)
- STONE, EDWARD JAMES (1831-1897)
- STONE, FRANK (1800-1859)
- STONE, GEORGE (1708—1764)
- STONE, LUCY [BLACKWELL] (1818-1893)
- STONE, MARCUS (184o— )
- STONE, NICHOLAS (1586-1647)
stone. Specimens were sent from See also:India to See also:England in the 18th See also:century, and were described in 1798 by the Hon. C. Greville under the name of corundum—a word which he believed to be the native name of the stone (See also:Hindi, kurund; Tamil,. kurundam; See also:Sanskrit, kuruvinda, " See also:ruby "). The finely coloured, transparent varieties include such gem-stones as the ruby and See also:sapphire, whilst the impure granular and massive forms are known as See also:emery. The See also:term corundum is often restricted to the remaining kinds, i.e. those crystallized and crystalline varieties which are not sufficiently transparent and brilliant for ornamental purposes, and which were known to the older mineralogists as " imperfect corundum." Such varieties were termed by J. See also:Black, in See also:con-
sequence of their hardness, adamantine spar, but this name is now usually restricted to a See also:hair-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 corundum, remarkable for a pearly sheen on the basal See also:plane.
Corundum crystallizes in the hexagonal See also:system. In fig. r, which is a See also:form of ruby, the See also:prism a is combined with a hexagonal See also:pyramid n, a rhombohedron R, and the basal pinacoid C. In
fig. 2, which represents a typical crystal of sapphire, the prism s is associated with the acute pyramids b, r, and a rhombohedron a. Other crystals show a See also:tabular See also:habit, consisting usually of the basal pinacoid with a rhombohedron, and it is notable that this habit is said to be characteristic of corundum which has consolidated from a fused magma. Corundum has no true
deavage, but presents parting planes due to the structure of the crystal, which have been studied by Prof. J. W. See also:Judd.
Next to See also:diamond, corundum is the hardest known mineral. Its hardness is generally given as 9, but there are slight See also:variations in. different stones, sapphire being rather harder than ruby, and ruby than See also:common corundum. The See also:colours are very varied, and it is probable that See also:iron is responsible for many of the tints, though See also:chromium is a possible See also:agent in certain cases. The transparent varieties are often distinguished as " See also:Oriental " stones. (See RUBY and SAPPHIRE.) Corundum is used largely for See also:watch-jewels, and for See also:bearings in See also:electrical apparatus.
The coloured corundums See also:fit for gem-stones come chiefly from See also:Ceylon, See also:Burma, See also:Siam and See also:Montana. Coarse dull corundum is found in many localities, and usually has higher commercial value as an abrasive agent than emery, which is less pure. The coarse corundum, however, is often partially hydrated or other-See also:wise altered, whereby its hardness is diminished. In India, where the native lapidaries use corundum-sticks and rubbers formed of the powdered mineral cemented with See also:lac, it occurs in the See also:Salem See also:district, See also:Madras, in See also:Mysore and in See also:Rewa. Large deposits of corundum exist in the See also:United States, especially in N. Carolina and See also:Georgia, where they are associated with peridotites, often near contact with See also:gneiss. The mineral has been extensively worked, as at Corundum See also:- HILL
- HILL (0. Eng. hyll; cf. Low Ger. hull, Mid. Dutch hul, allied to Lat. celsus, high, collis, hill, &c.)
- HILL, A
- HILL, AARON (1685-175o)
- HILL, AMBROSE POWELL
- HILL, DANIEL HARVEY (1821-1889)
- HILL, DAVID BENNETT (1843–1910)
- HILL, GEORGE BIRKBECK NORMAN (1835-1903)
- HILL, JAMES J
- HILL, JOHN (c. 1716-1775)
- HILL, MATTHEW DAVENPORT (1792-1872)
- HILL, OCTAVIA (1838– )
- HILL, ROWLAND (1744–1833)
- HILL, SIR ROWLAND (1795-1879)
Hill, See also:Macon See also:county, N.C., near which, in 1871, were discovered numerous rubies, sapphires and pebbles of coarse corundum in the See also:bed of a See also:river. Corundum occurs also at many localities in Montana, where the crystals are often of gem quality. They are found mostly as loose crystals in See also:gravel, but are known also in igenous rocks like See also:andesite and lamprophyre. Prof. J. H. See also:Pratt, who has studied the occurrence both in Montana and in N. Carolina, considers that the alumina was dissolved in a molten magma, from which it separated at an See also:early See also:period of consolidation, as illustrated by the experiments of J. Morozewicz. Corundum occurs also in See also:Canada in an igneous See also:rock, a See also:nepheline-See also:syenite, associated with Laurentian gneiss. Important deposits were discovered by the See also:Geological Survey in 1896, in See also:Hastings county, See also:Ontario; and corundum is now worked there and in See also:Renfrew county. New See also:South See also:Wales, See also:Queensland and See also:Victoria are other localities for corundum. The mineral is found also in the Urals and the Ilmen Mountains, in the See also:Alps (in See also:dolomite), in the basalts of the See also:Rhine, and indeed as a subordinate rock-constituent corundum seems to enjoy a wide See also:distribution, being found even in the See also:British Isles.
See See also:Joseph See also:Hyde Pratt, "Corundum and its Occurrence and Distribution in the United States," Bulletin U.S. Geol. Surv., No. 269 (1906); T. H. See also:- HOLLAND
- HOLLAND, CHARLES (1733–1769)
- HOLLAND, COUNTY AND PROVINCE OF
- HOLLAND, HENRY FOX, 1ST BARON (1705–1774)
- HOLLAND, HENRY RICH, 1ST EARL OF (1S9o-,649)
- HOLLAND, HENRY RICHARD VASSALL FOX, 3RD
- HOLLAND, JOSIAH GILBERT (1819-1881)
- HOLLAND, PHILEMON (1552-1637)
- HOLLAND, RICHARD, or RICHARD DE HOLANDE (fl. 1450)
- HOLLAND, SIR HENRY, BART
Holland, Economic See also:Geology of India (2nd ed.), See also:part i. (1898). (F. W.
End of Article: CORUNDUM
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