Inorganic Gemstones

Apatite

Rough Apatite

With a value of only 5 on the Mohs scale of hardness, apatite is seldom faceted as a gemstone, except for collectors. However, when cut correctly, stones are bright with strong colours. Transparent to opaque, apatite occurs as colourless, yellow, blue, violet or green hexagonal prisms or tabular crystals.

Apatite is an abundant mineral, found in many types of rock, but most gem-quality material is associated with pegmatites. Blue Burmese apatite is strongly dichroic, and shows colourless or blue when viewed from different directions. Fibrous blue apatite from Burma and Sri Lanka may be cut “en cabochon” to show a cat’s –eye. Chatoyant stones are also found in Brazil, along with yellow, blue and green varieties. Other localities include the Kola Peninsula (Russia), Canada, East Africa, Sweden, Spain and Mexico.

Spanish apatite is often called “asparagus stone”, due to its yellowish green colour.


Properties
Chemical Composition: 
Calcium phosphate with some chlorine or fluorine. Ca(F,Cl)Ca4(PO4)3
Classification / Type: 
-
Colors / Varieties: 
All colors. Chatoyant variety is very common.
Crystal System / Forms: 
Hexagonal System / Generally as six sided prisms with pyramidal and / or pinacoidal terminations, commonly as contact twins.
Hardness: 
5
Specific Gravity: 
3.15 - 3.23
Cleavage / Fracture: 
2 directional basal and prismatic cleavage / conchoidal fracture
Optic Character: 
Anisotropic, D.R.; Uniaxial negative (pseudo biaxial optic figure possible).
Lustre: 
Vitreous.
Refractive Index / Birefringence: 
1.642 - 1.646 / 0.002 - 0.006. Range: 1.637 - 1.651
Pleochroism: 
Weak, except in Burmese (Myanmar) gemstones.
Dispersion: 
0.013
Magnification: 
Fibrous inclusions, parallel black needles or canals, liquid fingerprints, phase inclusions and crystals.
U.V. Fluorescence: 
Varies according to color under ultra violet light.
Spectrum: 
Generally, a series of lines at around 580nm and 520nm in the yellow-green, with other lines at 512nm, 491nm and 464nm may be seen. Rare earth didymium spectrum composed of mainly the elements praseodymium and neodymium. Blue apatite may not show spectrum, sometimes.
Cause of Color: 
  • Yello green - rare earth elements
  • Blue - manganese.
Treatment (Enhancement): 
-
Specific Tests & Remarks: 
  • Attacked by hydrochloric and sulphuric acid.
  • Reacts to heat and may lose color.
Synthesis: 
Synthesized for use in lasers but cut synthetics are not sold commercially.
Simulants (with key separation tests): 
  • Transparent varieties can simulate a number of different gemstones with respect to their color.
  • Apatite cat's eye: Quartz (R.I., S.G., spectrum, inclusions), Chrysoberyl (R.I., S.G., spectrum, inclusions), Glass (inclusions), etc.
Geological Occurrence: 
Found in pegmatite, hydrothermal veins and cavities, metamorphic rocks in gem gravels.
Sources: 
Sri Lanka, Myanmar, Norway, Canada, India, Germany, Pakistan, Madagascar, Tanzania, Brazil.
Cuts & Uses: 
Facetted cuts, cabochon, beads, carvings, etc.

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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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