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FIRE IN THE EARTH
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and
it was found that, basically, the structure of the diamond was due to
an arrangement of the atoms in groups: one atom in the center of a
four-sided pyramid, or "tetrahedron," with four other atoms regularly
spaced around it to form the corners. The atom in the center of one
pyramid was, in turn, at the "peak" of the next one, and this
arrangement repeated itself countless billions of times in the
smallest of diamonds.)
Sometimes
a crystal is flattened or elongated in one direction because of
irregularities of growth; and it frequently is difficult to decipher
the form. Flat faces of the octahedron are usually marked by platy
growths and by minute triangular pits which, when viewed with a
magnifying glass, are delicate and beautiful. Diamonds are usually
found as isolated single crystals bounded on all sides by faces, which
indicates that they did not grow attached to a matrix, like crystals of
quartz, beryl, topaz, and other minerals. An inter-growth or marriage
of two crystals is not uncommon but the intergrowth is often so
intimate that it is not always easy to detect. These are known as the
twins, or twinned crystals. They are characteristic of the spinel or
spinel twin we were talking about previously.
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In size, diamond crystals usually are quite small. An octahedron
weighing one carat measures about a quarter of an inch across, and this
is well over the average size. Of course, there have been large ones.
The largest crystal ever found, and that in South Africa, was the
"Cullinan" diamond, which measured 4 by 2-1/2 by 2 inches and weighed 3106 metric carats, or 1 1/3 pounds. Other crystals may be 1/4 millimeter
down to microscopic dimensions. Here are what are believed to be the
ten largest diamonds discovered, as shown in metric carat sizes:)
(10)
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