Nonmetals Native Elements,
the Diamond

Diamond Composition. Pure carbon

Crystallization. Isometric, normal. Crystals are usually octahedral in habit, but the faces are commonly curved or pitted (Fig.206). Curved faces of the hexoctahedron are frequently observed (Fig. 207) Cubic and dodecahedral planes rate. Twins, with the octahedron as twinning plane (Fig. 208); often flattened.

Structure. Usually in crystals, but commonly distorted into elongated and irregular forms. At times in spherical forms with radiating structure. Rarely massive.

Physical Properties. Perfect cleavage parallel to the octahedral faces. H. = 10 (hardest substance known). G. =3.5. Luster adamantine or greasy. Usually colorless or pale yellow.

Also pale shades of red, orange, green blue and brown. Rarely in deep shades of blue, red or green; at times black. Usually transparent bur may be translucent or opaque. Very high index of refraction (diamond = 2.42, quartz =1.55) Strong dispersion of light. Electrified by friction and becomes phosphorescent when rubbed with a cloth. Some stones after exposure to sunlight give off a phosphorescent glow in the dark.

Varieties. Ordinary, In rounded crystals , some of which are perfectly transparent and colorless (first water). Others are faintly colored in various shades and frequently contain inclusions and are flawed. Bort. In rounded spherical forms with radiating structure or made up of confused crystalline aggregates; usually gray, brown or black in color and translucent to opaque. Fragments of crystals that are unavailable for cutting are also frequently called bort. Carbonado or black diamond. Massive with crystalline structure or granular to compact without cleavage. Black or grayish black; opaque.

Tests. To be distinguished by its great hardness, its adamantine luster and its octahedral cleavage. Burns at a high temperature to CO2 gas, leaving no ash. Will burn readily in oxygen gas giving off a brilliant light.

Occurrence. The diamond is a rare mineral. It has been found in many different localities, but only a few have furnished the mineral in notable amount. Most commonly the diamond is found in the sands and gravels of stream beds, where it has been preserved by its great hardness and fairly high specific gravity. In South Africa and recently in Arkansas kit has been found embedded in masses of an igneous rock, know as periodotite, Three countries have up to the present furnished practically the entire world’ output of diamonds, namely, India, Brazil and South Africa.