194 DESCRIPTIONS OF MINERALS. 



Xext 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 Tallied at the price of a diamond 

 of the same size. They seldom exceed half an inch in their 

 dimensions. Two splendid red crystals, as long as the little 

 ringer and about an inch in diameter, are said to be in the 

 possession of the king of Arracan. The 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 occur of much larger size. According to 

 .^iian, SirAbram 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 

 ornery diminishes its hardness, and consequently its abrasive 

 power ; pulverized corundum is more valuable and efficient 

 in abrasion. 



Diaspore. Hydrated aluminum of the formula Al 4 H 2 =Water 14'9, 

 alumina 85*1 =100. Usually found associated with corundum. Crys- 

 tals usually thin and flattened. Color whitish, grayish, pinkish, etc. 

 Very brittle. Translucent. H. 0-5-7. Cr. 3 '5. From the Urals; 

 Schemnitz ; Chester, Mass. ; Chester County, Pa. ; Xorth Carolina. 



Gibbsite (Hydrargillite). Hydrated alumina ; Al 6 H 6 = water 34*5, 

 alumina 65 '5=100. Occurs in hexagonal crystals ; more commonly in 

 stalactitic axd 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. =2"3-2*4. 

 2s ear Slatoust in the Ural ; in Asia Minor ; on corundum at Unionville, 

 Pa. ; at Richmond, Mass. in stalactitic forms ; in Orange County, X. Y. 



Hydrotalcite ( Vulknerite, 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 



