Nicholas Priznar, age 9, of Cohoes, N.Y.,for his question:
What shape is a natural diamond?
The most famous diamond fields in the world are in South Africa, They were discovered because children the world over like to play with pretty pebbles. About 100 years ago, the children of a Boer farmer found some pretty pebbles in the sandy bed of the Vaal river. These treasures were not shaped like the glittering diamonds in a precious necklace, or like the sparkling diamond in a ring. It took an expert to spot them and recognize them as rough, or natural, diamonds.
Diamond, the hardest of all natural stones, the brightest of all gems, is formed in the earth's crust. It is a crystal form of the plentiful element carbon. But Mother Nature was sparing about making her diamonds and rather careless about the shapes of the precious crystals. Diamonds are very rars stones and we find the natural stones in several different shapes.
Most of the natural stones are smaller than peas and the brilliant crystal is usually covered with a dull, greyish film. In a diamond mine, many carloads of earth or rock must be sorted to find one little gem. Chances are, its shape will be octahedron. This is an eight‑sided figure which looks like two little pyramids set base to base. A natural diamond also may be shaped like a cube, a six‑sided figure of equal squares.
Natural diamonds also occur in round balls called ballas. Sometimes Mother Nature makes her diamond material in careless black lumps or masses. These lumps are called carbonado, Other natural diamonds occur as small, flat triangles. One of the most amazing of natural diamonds is the hexoctahedron. This is a ball‑shaped crystal with its entire surface covered with small, slightly humped triangles.
Altogether, there are 48 of these surface triangles, all of equal size.
Less than a quarter of the natural diamonds will become gem stones4 The rest will be discolored or cracked with flaws. These will be used in industry to cut and grind and polish hard metals. Some even will be used to out and polish the precious gem stones, for only diamond can out diamond, The gem stones are measured in carats. A diamond of one carat weighs a gram. It takes about 28 of them to weigh one ounce. This one carat diamond measures ebout six and a half millimeters, or roughly one quarter inch across.
The biggest diamond found was named the Cullinan. It was discovered in South Africa in 1905. Its weight was 3,106 carats, roughly one and one third pounds. The Cullinan was cut into nine large gems and 96 smaller ones, But in its natural state, this biggest of all diamonds looked like a rather flat, irregular lump of glass covered with a gritty film of dull grey.