Indian Gujarati Bridal Wedding Jewellery Collection 20

Indian Gujarati Jewellery.
By Aamir Mannan.

2.DOUBLE REFRACTION AND DISPERSION

In some minerals the figures very somewhat; thus in zircon, while the blue, white, and golden 'fried' type most popular in moderan jewellery are almost constant in their birefringence of 0.059. many of the ceyclonese 

zircons. particularly the green varieties, have a much lower double refractions, sinking in some cases practically to zero. this peculiaity is unique amongst minerals, and will be discussed at greater length in the chapter on zircon. synthetic rutile has been manufactured in the USA (since 1949), and its anormous double refraction will be one means of identification. calcite, though not a gemstone, plays an important

part in gemmological instruments in its optocally pure form of 'ice land spar', how, apart from the refractometer, can one test whether a given stone doubly refractive or not? the simplest method of all, which with a little practice is quite easily carried out, is to examine the stone carefully with a powerful pocket lens-say giving 8x to 12x magnification. for example, look trougth the table facet of a zircon with a lens, and focus sharply on to the edges of the back facets where they adjoin the culet, and it will be noticed that instead of a single sharp line where the facets join.