This section is from "Scientific American Supplement Volumes 275, 286, 288, 299, 303, 312, 315, 324, 344 and 358". Also available from Amazon: Scientific American Reference Book.
This mineral occurs in great abundance in and about the tunnel, and from all the shafts. There are two forms occurring there, the most abundant of which is the rhombohedral, after Fig. 3. It can generally be obtained, however, in excellent crystals, which, although perfect in form, are opaque, but often large and beautiful. It is always packed with a thousand or its multiple of other crystals into veins of a few inches thick; and crystals are obtained by carefully breaking with edge of the cold chisel these masses down to the fundamental form shown. As the masses are never secured by the miners, they can always be picked from the piles of débris around the shafts and the dumps, and afford some little instruction as to the manner in which a mineral is built up by crystallization, and may be subdivided by cleavage to a crystal of the same shape exactly, but infinitesimally small. A crystal to be worth preserving should be about an inch in diameter, and as transparent as is attainable.
Another form of calcite which is to be sparingly found is what is called dogtooth spar, having the form shown in Fig. 4. They occur in clear wine-yellow-colored crystals, from a quarter to half an inch in length; they occur in the chlorite in geodes of variable sizes, but generally two and a half inches in diameter, and which, when carefully broken in half, showed beautiful grottoes of these crystals. The few of these that I have found were in the four-foot vein of chlorite down the Shaft No. 1, to the west of the shaft about one hundred and fifty feet, and on the south wall; it may be readily found by probing for it, and then the geodes by digging in. There need be no difficulty in finding this vein if these conditions are carefully considered, or if one of the miners be asked as to the soft vein. Both these forms of calcite may be distinguished from the other minerals by first effervescing on coming in contact with the acids; second, by glowing with an intense (almost unbearably so) light when heated with the blowpipe, but not fusing. Their specific gravity is 2.6, or near it, and hardness about 3, or equal to ordinary unpolished white marble.