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Sec. II, Ch. 1: The Diamond

Sec. II, Ch. 1: The Diamond Page of 366 Sec. II, Ch. 1: The Diamond Text size:minus plus Restore normal size   Mail page  Print this page
58                                   The Diamond.
i.e., red, yellow, and blue, definitely separated one from the other in these little circles, and if their number were considerable, and they stood at equal distances from each other, then he pronounced the Brilliant to be well cut.
The effulgency of a good Brilliant largely depends on the fact that by the small " critical angle " of a Diamond (24° 13' ) much of the light which enters the stone, instead of passing through it, is " totally reflected " from some of the facets, and thus returns to the eye of the observer. In the Rose Diamond the light is reflected from the under-plane.
As the Diamond is a mineral which crystallizes in the cubic system, it does not, in its normal condition, possess the power of double refraction, neither does it polarize light ; but Sir David Brewster long ago shewed that there are in many stones certain optical irregularities due to internal air-bubbles, cavities, or other flaws. The vapour or gas in these minute cavities is pent up under intense pressure, and the Diamond is thus thrown locally into a state of tension, which gives rise to double refraction. So great is the internal strain in some Diamonds, that they explode when unearthed from their matrix and brought up from the mine, especially when held in a warm hand, which naturally tends to expand the included gas.
Lustre and Colour.
The lustre of the Diamond is of that peculiar, indescribable, but well-known character termed adamantine. The surface of the native crystal is often rough, and has a peculiar leaden grey semi-metallic lustre.
The Diamond in its purest condition, is colourless and transparent ; yet at times it is found coloured throughout
Sec. II, Ch. 1: The Diamond Page of 366 Sec. II, Ch. 1: The Diamond
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