194 DESCRIPTIONS OF MINERALS. 
_ Next to the diamond, the sapphire in some of its varieties 
is the most costly of gems. ‘The red sapphire is much more 
highly esteemed than those of other colors. A crystal of 
one, two or three carats is valued at the price of a diamond 
of the same size. ‘hey seldom exceed half an inch in their 
dimensions. ‘l'wo splendid red crystals, as long as the little 
finger and about an inch in diameter, are said to be in the 
possession of the king of Arracan. he largest oriental ruby 
known was brought from China to Prince Gargarin, gov- 
ernor of Siberia; it afterward came into the possession of 
Prince Menzikoff, and constitutes now a jewel in the im- 
perial crown of Russia. 
Blue sapphires oceur of much larger size. According to 
Allan, Sir Abram Hume possessed a crystal which was three 
inches long. One of 9°51 carats is stated to have been found 
in Ava. | 
Corundum and emery are crushed to a powder of differ- 
ent degrees of fineness, and make the abrading and polishing 
material called in the shops emery. ‘The iron oxide of true 
emery diminishes its hardness, and consequently its abrasive 
power ; pulverized corundum is more valuable and efficient 
in abrasion. 
Diaspore Uydrated aluminum of the formula AlO, H,=Water14°9, 
alumina 85'1—100. Usually found associated with corundum.  Crys- 
tals usually thin and flattened. Color whitish, grayish, pinkish, etc. 
Very brittle. Translucent. H. 65-7. G. 35. From the Urals; 
Schemnitz ; Chester, Mass.; Chester County, Pa.; North Carolina. 
Gibbsite (Hydrargiliite). Hydrated alumina ; Al O, He=water 34°5, 
alumina 65°5—100. Occurs in hexagonal crystals ; more commonly in 
stalactitic aad mammillary forms, with smooth surface, looking like 
chalcedony. Color white, grayish and greenish-white ; translucent, 
sometimes transparent when in crystals, H.=—2°5-3°5; G.=%-3-2°4. 
Near Slatoust in the Ural ; in Asia Minor ; on corundum at Unionville, 
Pa.; at Richmond, Mass. in stalactitic forms ; in Orange County, N. Y. 
Hydrotaicite ( Vilknerite, Houghite). A soft pearly mineral, contain- 
ing alumina, magnesia, and water. Accompanies spinel, and some- 
times a result of the alteration of spinel crystals. Occurs near Sla- 
toust ; at Snarum, Norway; near Oxbow in Rossie, St. Lawrence 
County, N. Y. (the variety Houghite). 
Spinel. 
Isometric. In octahedrons, more or less modified. Fig- 
ure 4 represents a twin crystal. Occurs only in crystals ; 
cleavage octahedral, but difficult. 
Color red, passing into blue, green, yellow, brown, and 

