06 MINERALOGY. 
lustre so much admired. Colorless diamonds are most esteemed as orna. 
ments. The impure and small diamonds are reduced to powder to be used 
in grinding the rest. The grinding of the diamond requires great skill, and 
the different forms imparted have definite names. The principal of these 
are: 1, The brilliant (pl. 32, figs. 85, 87, 90); 2, The rosette or rose 
( figs. 84,91). Older forms, now rarely imitated, are shown in figs. 80, 81, 
82, 83, and 86. 
The second form of carbon is graphite, known also as plumbago and 
blacklead. It also occurs so pure as to leave but little ash when burned. 
Certain characteristics distinguish it very decidedly from the diamond : it 
does not crystallize in the regular system, but in six-sided plates ; is a good 
conductor of electricity; and has a low specific gravity, 2.14—2.27. 
Graphite is soft, unctuous to the touch, of a steel-grey metallic lustre, and 
opake. In thin plates it is flexible. It occurs in beds and layers in 
primitive rocks, gneiss, granite, primitive limestone, greywacke, and 
greenstone. The principal localities are in England, Germany, Norway, 
Greenland, France, Spain, the United States, &c. Its uses are various, 
being employed in fabricating pencils, in the construction of crucibles and 
small furnaces, as an anti-attritient, &c. The best graphite for the manu- 
facture of lead pencils comes from the Borrowdale mine, England. The 
poorer graphite is extensively used, and, by pressure, good pencils are 
made. 
The third kind of carbon, the uncrystallized, which occurs in various 
combinations with hydrogen and oxygen, will be discussed under the head 
of Geology. 
Class 2. Native Metals. 
Simple bodies, or occurring as mixtures or alloys with one another, in 
variable or indefinite preportion; specific gravity from 7 to 22. All 
possess a metallic lustre, or at least acquire it under the burnisher. They 
are opake, and good conductors of electricity. 
1. Native Iron. 
Iron rarely occurs in the native or uncombined condition. It is found 
as such in small masses or grains only in mica slate, and in large masses as 
meteoric iron. In its combinations with the other elements, and especially 
oxygen and sulphur, it is the most generally and abundantly diffused of all 
metals. Metallic iron was known in very ancient times, since Moses speaks 
of iron knives. With respect, however, to the manner in which the ancients 
vbtained their iron, we know little or nothing, except as far as it may have 
been derived from aerolites. Instead of iron the ancient Greeks used a 
mixture of tin and copper. Meteoric iron sometimes occurs in large masses. 
One of these, found in South America, weighed nearly 40,000 Ibs. Remark- 
able specimens, also, are found in the cabinets of St. Petersburg and Vienna. 
One in the cabinet of Yale College, at Newhaven, weighs 1635 lbs. 
However rare the fall of meteors may be, they are mentioned by as early an 
author as Pliny. The fact of their existence was subsequently doubted, 
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