Inorganic Gemstones

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Birefringence

The arithmetical difference between the refractive index of the ordinary ray (Omega) and that of the extra-ordinary ray (Epsilon) in the case of uniaxial minerals and that between the alpha and gamma in the case of Biaxial, at their maximum divergence, is known as the birefringence or double refraction. The following examples illustrate the above principle.

Optic Character Gemstone Refractive Index Birefringence (D.R.)
Isotropic Diamond 2.418 -
Isotropic Fluorite 1.434 -
Anisotropic Corundum 1.762 - 1.770 0.008
Anisotropic Peridot 1.654 - 1.690 0.036
  • This is a property characteristic of anisotropic gemstones.
  • The optic axis is a direction of single refraction hence no birefringence is seen in this direction.

A stone with higher birefringence will exhibit doubling. Inclusions, facet edges or an object viewed through the stone will appear double. A good illustration of double refraction occurs in transparent calcite. An object observed through an anisotropic substance will show double edges or a double image.


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In Germany, the garland of ambers is hung around the necks of the infants, so that their teeth might come out without much trouble.

In Turkey, people fix a piece of amber in the hubble-bubble, dogged by an age old belief that the presence of the jewel would destroy all the germs and no disease would spread, even after many have dragged their puffs from it.

In Greece, people think if wine is poured into the cups made of amethyst, one does not get drunk after drinking that.

In Rome, a talisman having coral pieces is considered very auspicious to quell the bad spells of evil look. The Romans were in the habit of hanging chains made of ancient coral pieces from the cradle of the infants to protect them from evil effects.

In China, people wear rings studded with tiny conch or oyster shells as they believe it cures all aches such as stomach ache, worms and like.

In India, pendants made of silver and studded with pearls are hung from the necks of the children to save them from any bad effects.

Greeks still believe, if women wear blue sapphires then no sense of immorality would pollute their mind nor can any fear of the supernatural can trouble them.

The Pope Innocent III had circulated an order asking all the priests wear blue sapphire, so that morality can be strengthened.

It is said about turquoise, that when the stone changes its color into yellow, it actually signals bad times to the person who wears it.

It is believed that a turquoise gifted to a friend or a lover turns his or her life into one of happiness and good luck.

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