During many centuries the pearls were perceived as a gift of nature and destiny and traditionally ranked as jewels.
Ancient Greeks believed that nacreous stones are the nymphs’ solidified tears. Like nymphs, the special sort of molluscs-zhemchuzhnits lives in the warm seas: at the coast of Arabian peninsula, Ceylon, Northwest Australia, Southern Burma, many islands of Pacific Ocean, Central and the South America, Japan. In Europe collected river pearls: first of all in Russia, England, and Ireland. When the alien body occurs inside the shell, for example a grain of sand, zhemchuzhnitsa perceives it as a trauma and starts to “cry” with nacreous tears, enveloping an alien subject with the aragonite layers. So the pearls are born. During 2-3 years the oyster increases round the object a layer in 5 mm. To grow up a pearl of the average size is required nearly 3-4 years, large – 12 years, huge – more than 200.
Colour of pearls depends on the impurities in the aragonite, and also from the degree of the transparency of an external cover and the character of a spreading layer. In nature the pearl amazes with its variety of forms and colours. A colour variety of “nacreous stones” fluctuates from rich-black and green from Gulf of Mexico islands and Tahiti to bright-pink – from California gulf, silver and yellow – at coast of Ceylon, pale-green – in Japan and white – in Australia. Shades are countlessly. Depending on the size, the pearls are subdivided on high-quality – more than 3 mm, beads – 3-2 mm and a pearl dust – less than 2 mm. According to the form, colour and shine there are 3 classes of pearls: I class – absolutely round, white with strong shine, with a weak bluish or pinkish shade; drop-shaped, the faultless form are equated to the round; II class – not ideally round (pear-shaped, oval, slightly flattened), white with strong shine and absolutely round white with weak shine; III class – all pearls with weak shine which are suitable for manufacturing of jewellery at least in small degree.
Colour of pearls has its price: it is considered the most expensive is bright-pink and black, and the cheapest is yellow. As pearl’s unit of weight it is accepted pearl gran – remained in gemology for measuring of pearl’s weight, the stand-alone unit equal of 50 mg (0,25 carats).
Today distinguish three kinds of pearls: natural – it is formed without participation of the man, cultivated – the alien body is put into the mollusk’s shell by the man, and artificial.