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mentioned below, but the diamond satisfies all the conditions and is highly esteemed as a gem.
(i) The splendour or beauty of a stone depends on its colour, lustre, play of colours and brilliancy or fire. These
properties are discussed in detail in a separate chapter. A coloured
diamond has all these properties, but it is very rare. Rubies and
emeralds have beautiful colours but they lack brilliancy and fire. Opal
is attractive only due to its play of colours. The rough stones are
often dull pebbles, but cutting and polishing improve their properties.
Hard stones take a better polish than the soft ones.
(ii) Durability.—Precious
stones should be at least harder than dust particles in the air. So
they must be harder than quartz, or they are easily scratched and wear
out quickly. Diamond, ruby, emerald and sapphire are harder than quartz.
(iii) Rarity.—This is a valuable attribute to gems and has been discussed already.
(iv) Fashion.—Fashion
plays a great part in the value of gems. A gem may be very popular at
some period and fall into desuetude at another period. Some colours are
always liked, e.g. blue, red and green, whereas yellow is not much
liked. Ruby, sapphire and emerald have been very popular in South
India, but diamond has now become the fashion with the middle and
richer classes. Certain stones attain local popularity due to their
production and easy availability there.
Mineralogy and Gems
Gems
are mostly mineral species. Methods applicable to the study of minerals
could be applied to identify gem-stones, and are dealt with in
Text-books of Mineralogy and Treatises on Gem-stones. The most valuable
publication in this line is Max Bauer's Edelsteinkunde, which was translated by L. J. Spencer in 1904. There is a recent
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