By Ralf Tappert
Diamonds in Nature: A advisor to tough Diamonds illustrates the variety of crystal shapes, shades, floor textures, and mineral inclusions of tough, uncut, clearly forming diamonds. each one bankruptcy includes images that convey the original actual features of the diamonds, and the accompanying textual content describes the techniques that resulted in their formation. This booklet is a useful reference guide for pro geoscientists—including gemmologists and exploration geologists.
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Additional info for Diamonds in Nature: A Guide to Rough Diamonds
In the most basic arrangement, single nitrogen atoms replace single carbon atoms during the growth of the diamond. 33 Single substitutional nitrogen atoms are eﬀective color centers, and even small amounts (<100 ppm) cause an intense yellow color that is referred to as canary yellow (Fig. 83 Very few mantle-derived diamonds contain single substitutional nitrogen atoms, and if they do, the single substitutional nitrogen usually occurs together with nitrogen in aggregated states. 71, 72 The presence of relictic single substitutional nitrogen atoms in natural diamonds, therefore, is a sign that the diamonds were transported to the Earth’s surface shortly after their formation.
In some cases, the inward curvature is so extreme that the diamond develops a skeletal appearance. These diamonds are referred to as re-entrant cubes (Fig. 2-14, Fig. 282 Diamond cubes with crystal faces that have a strong outward curvature can develop a rounded form that resembles a tetrakis-hexahedron (Fig. 2-16). Because they lack ﬂat, crystallographically bound crystal faces, diamond cubes are sometimes referred to as cuboids. Although the cubic habit is found among monocrystalline diamonds, it is particularly common among ﬁbrous diamonds.
37 THE MORPHOLOGY OF DIAMONDS 2-50: Ballas: a spherical variety of ﬁbrous diamond. 18 ct). 2-51: Relationship between coat thickness and habit of an octahedral diamond with a ﬁbrous coat. A. uncoated B. thin coat C. thick coat D. 19 ct). The octahedral crystal faces are marked by numerous trigons. 38 B C D THE MORPHOLOGY OF DIAMONDS 2-53: Polished section through a sharp-edged octahedral diamond with a thick ﬁbrous coat (Ø: ~7 mm). The ﬁbrous coat exhibits faint concentrical layering. sign of rapid growth from highly carbon-oversaturated ﬂuids.