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ordinarily
light, yet hard and silver-white metal. With aluminium, it produces an
alloy which is hard, strong and light material for the construction of
aeroplanes and airships. The transparent and coloured varieties, e.g.
emerald, and aquamarine form valuable gem-stones. Precious beryl and
aquamarine show well in artificial light.
Grades
Beryl
proper commands very little value as a gem-stone. But the coloured and
transparent varieties, e.g. emerald and aquamarine form valuable
gem-stones. Because of its rich colour and the rarity of fine quality
material, emerald is the costliest gem-stone. Its refrac-tivity and
dispersion are weak. It has neither brilliancy nor fire. The green
colour is due to chromium. Aquamarine is transparent, and its colour
varies from pale blue to sea-green. Heat treatment is said to improve
the colour of these stones. When pure it is of a golden-yellow colour
and it is then known as golden beryl.
The
emerald has been known amongst the Hindus as 'Marakata' and as coming
from the Black Sea coast. It was also known in Europe at the time. They
considered genuine emeralds as infallible remedies for all cases of
poisoning. These stones are also divided into four castes, each being
recognized by certain peculiarities of shade and other marks. The green
colour of the emerald was considered to be due to chromium, but is
also believed to be due to some organic substance, perhaps abstracted
from its matrix, which contained organie remains. The Tagore family and
other notables are said to possess good specimens of emerald. Heliodor
is a variety of yellow beryl from south-west Africa. Morganite, also
known as Vorobievite, is a pink or rose-red beryl. Flawless emeralds of
good colour are extremely rare and are very valuable. Owing to
inclusions they have a massive appearance. Emerald
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