Huitpan, or single cut. 16 facet " double " 24 " " single brilliant. Cabochon " carbuncle. Star cut, fig. 9. Degree or rose cut, fig. 10. The last two beautiful forms of cutting are frequently given to fine paste or imitation diamonds. Of late years nearly all gems have been cut quite round, and in many instances with a sacrifice of size and brilliancy. DIAMOND. The diamond is one of the most precious minerals, and yet it consists of pure carbon, the most common substance that is known, a substance that is present in all animal and vegetable bodies and in the larger number of minerals. When carbon is crystallized the result is the diamond, which is always found in detached crystals, either octahedrons or rhombic dodecahedrons, the planes of the angles being often convex or rounded,—this curving crystal being peculiar to the diamond. The cleavage is perfect, and, parallel to the faces of the octahedron, the fracture is conchoidal or curved. The diamond is not acted upon by acids or alkalies, is infusible but combustible, and burns under heat of a very high temperature. Diamond powder burns readily, but larger pieces are not affected by the blow-pipe. The diamond is a non-conductor of electricity, but acquires positive electricity when rubbed, and retains it for half an hour. After being exposed to the solar rays, the diamond presents a distinct phosphorescence in the dark. It possesses single refraction, but belongs to those bodies which reflect light most strongly, and its magnifying power is much greater than that of glass; it does not polarize light; its lustre is adamantine, and specific gravity 3.5 to 3.6. The diamond is the hardest of all known minerals, ranking No. 10 in Moh’s scale of hardness. White, and the different shades from very light yellow to dark yellow or canary, comprise, according to the popular idea, the colors of the diamond. Yet the diamond is found in green, red, blue, brown, olive, orange, and black, and also in the various shadings of these colors and in opalescent tints. As the limpid or white diamond surpasses all other white stones in the power of its lustre and the magnificence of its fire, so do the colored diamonds outrank the emerald, ruby, sapphire, and other gems of like colors. Colored diamonds, excepting light yellow and brown, are rare, and hence are the most valuable of precious stones. The limpid or perfectly white and the white with a bluish tint are the most sought after, while fine deep golden yellow or canaries and pronounced fancy colors always find a ready market. Diamonds come principally from the mines in South Africa; some are found in Brazil and India, and fewer in Sumatra, Borneo, the Ural Mountains, and Australia. Crystals have also been found in the United States. The amorphous or carbon diamond is found only in Brazil. The pebbles or masses are opaque, steel-gray to black in color, and sometimes weigh 1,000 carats.