MINER 



conchoidal. Alternates from transparent to translu- 

 cent ; and the translucent varieties frequently exhibit 



i . . i n -f. iii 



543 



a six-rayed coalescence. 



Con*/. Parts. 



Refracts double. 



lied Sapphire, or 

 Oriental Uuby. 

 90.0 



7-0 

 1.2 



Blue Sapphire. 

 Alumina, 92.0 

 Lime, . 5.25 

 Oxide of iron, 1.0 

 Loss, . 1.75 



1.8 



100 



Chevrnix, Phil. 

 Trans. 1802. 



100 

 Cttevenijc, Phil. 



Trans. 1802. 



Chemical Character. Infusible beforethe blowpipe. 

 Physical Characters. Becomes electrical by rub- 

 bing, and retains its electricity for several hours ; but 

 does not become electrical by heating. 



Geognottic Situation. It occurs in alluvial soil, in 

 the vicinity of rocks belonging to the secondary or 

 floetz-trap formation, and imbedded in gneiss. 



Geographic Situation. It occurs in alluvial soil, in 

 different countries of Europe, but most abundantly in 

 the East, as Ceylon, Pegu, &c. 



I'sft. This mineral is, next to diamond, the most 

 valuable of the precious stones. The most highly 

 prized varieties are the crimson and carmine red ; 

 these are the Oriental Ruby of the jeweller, and next 

 to the diamond, are the most valuable mineral- hither- 

 to dUcovered. The blue varieties, the Sapphire of the 

 jeweller, are. next in value to the red. The yellow 

 varieties, the Oriental Topaz of the jeweller, are of 

 less value than the blue or true sapphire. 



Emery. y- \irnv, Jameson. Schmiergi-1, H'crtur. 



1 ' racters. Colour intermediate between 



greyish-black and bluish-grey. Occurs massive and 

 MHfcatfd ; and the massive is sometimes intermix- 

 ither minerals. Lustre glistening, ]. 



ilamantine. Fracture fine and 

 -ometimes splintery. Slightly 

 ut-ent on 



'i'noi/ic in- .n/iic Situations. It is found 



in talc-slate at ( Kh-i nkopf near Schwartzenberg, and 

 L'lbensiock in Saxony. It occurs abundantly in the 

 isla -.<>s. 



I It is used for polishing hard minerals and 

 metals, and hence is an important article in the arts. 



THIRD S: 



Corundum. CORUNDUM, Jameson. Korund and Demant-Spath. 

 Wtntr. 



External Character*. Colours white, grey, green, 



I and brown. The green, blue, and red co- 



lours are generally muddy, and inclining to grey. 

 When cut in a semicircular form, it often presents an 

 opalescent itar of -ix ray. Its principal crytalliza. 

 tion* are six-sided prisms and six-sided pyrai 

 Externally they are dull and rough. Lustre of the 

 cleavage and fracture shining and glistening, and either 

 vitreous inclining to resinous, or pearly inclining to 

 adamantine. Fracture conchoidal, and sometimes un- 

 even. Alternates from strongly translucent to trans- 

 lucent on the edges. 

 Geognotlic and Geographic Situation*. Red and 

 blue corundum occur in dolomite in St. Gothard ; also 

 in the Carnatic, on the coast of Malabar ; and abun- 

 dantly in the neighbourhood of Canton in China. 

 U*e. In its powdered state, it has long been used 

 by the artists of India and China for cutting and po- 

 lishing precious stones. 



III. PRISMATIC CORUNDUM or CHRY&OBEHYL, 

 ornadum. Jamrscn. Kry,olitryll, firmer. Cymophane, Haiiy. 

 I'n-mati-< her Corund, Motis. 

 Prismatic. Priam = 104 41'. Cleavage prismatoi- 



in the direction of the smaller diagonal of the Oryctogno- 

 Hardness = 8.5. Specific v gy l_ 



A L G Y. 



dal, 



oblique four-sided prism. 



gravity = 3.7 3.8. 



External Characters. Chief colour asparagus green. 

 Often exhibits a milk-white opalescence, -which ap- 

 pears in general to float in the interior of the mineral. 

 Occurs in blunt angular rolled pieces, that sometimes 

 approach to the cubic form, and crystallized in six- 

 sided prisms. Internally splendent, and lustre inter- 

 mediate between resinous and vitreous, but more in- 

 clining to the first. Fracture perfect conchoidal. 

 Semitransparent, sometimes inclining to transparent, 

 and refracts double. 



L'onsiit. Parts. Alumina, . . 71.5 

 Silica, . . 18.0 



Lime, . 6.0 



Oxide of iron, . 1.5 



Loss, . . 3.0100 



According to Klaproth, b. i. s. 102. 



Geognoitic and Geographic Situations. It occurs in 

 BraziC in alluvial soil with topaz, or in sandstone with 

 diamond ; and at Haddam, on Connecticut River, in 

 the United States, in granite, along with garnets, beryl. 

 and tourmaline. 



It is found in the Uland of Ceylon, in the beds of ri- 

 vers, along with sapphires, rubies and tourmalines. 



Utet. This line gem was formerly much less prized 

 than it is at present. When cut and polished, it is not 

 inferior in brilliancy and beauty to other gems of the 

 same colour. 



GENUS IV. DIAMOND. 

 tilar. I lardness = 10. Sp. gr. =: 3.4 3.6. 



1. OCTAHEDRAL DIAMOND, Jameson. Octaedrischer Octahedral 

 Demant, Mohs. Diamond. 



Tessular. Cleavage octahedral. 



External Characters. Most common colours of the 

 diamond are white and grey. Besides these two colours, 

 it occurs blue, red, brown, yellow, and green. Oc- 

 'ystallized in octahedrons, tetrahedrons, 

 rhomhoidal dodecahedrons, and in various twin crystals. 

 Internally, is always splendent, often sj>ecular splen- 

 dent, and the ! adamantine. Seldom? 



completely tr insj arent ; more generally it rather in- 

 clines to semitransparent ; but the black variety is near- 

 ly opaque. ltel'racts -ingle. 



lituriit I'nrtt. Is said to be nearly pure carbon. 



GeogHOilic Situaliim. It occurs in imbedded grains 

 and crystals, in alluvial soil, sandstone, and, it is said, 

 in secondary trap-rocks. 



Geographic Situation It occurs in Brazil, Peninsu- 

 la of India, and the island of Borneo. 



Utet. The diamond, on account of the splendour of 

 its lustre, its peculiar play of colour, its hardness, and 

 lastly, its rarity, is con-idered as the most precious sub- 

 stance in the mineral kingdom, and is particularly va- 

 lued by jewellers. The diamonds purchased by jewel- 

 lers are generally in grains, or crystal*, and sometimes 

 coarsely polished. Vide Article DIA MOND, for a full ac- 

 count of various sizes of the diamond. 



DIAMOND. 



. TOPAZ. TOPAZ. 



Prismatic. Axifrangible. Hardness = 8. Sp. gr. = 

 3.*, 3.6. 



1. PRISMATIC TOPAZ, Jameson. Prismatischer Toprz, Pi-lunatic 

 3/0/1*. Topaz. 



Prismatic. Pyramid = HI 7': 101 52': 90 55': 

 Prism = 124 19'. Cleavage axit'nin-ible. 



This species contains three sub'pecies, viz. Common 

 Topaz, Schorlite, and Physalite or Pyrophysalite. 



FIRST SUBSPFI 



COMMOX TOPAZ. Topaz, Werner. Common 



External Character!. Colours yellow, green, blue, To l >; '* 

 and red. Frequently crystallized, and generally in 



