Apatite

apatite
Apatite rough and sphere

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 into 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.

Apatite Pictures

Apatite-nepheline mineral Apatite rough

Cause of Color :
  • Yello green – rare earth elements
  • Blue – manganese.
Chemical Composition :

Calcium phosphate with some chlorine or fluorine. Ca(F,Cl)Ca4(PO4)3

Crystal System / Forms :

Hexagonal System / Generally as six sided prisms with pyramidal and / or pinacoidal terminations, commonly as contact twins.

Cuts & Uses :

Facetted cuts, cabochon, beads, carvings, etc.

Dispersion : 0.013
Hardness : 5
Lustre : Vitreous.
Magnification :

Fibrous inclusions, parallel black needles or canals, liquid fingerprints, phase inclusions and crystals.

Optic Character :

Anisotropic, D.R.; Uniaxial negative (pseudo biaxial optic figure possible).

Pleochroism : Weak, except in Burmese (Myanmar) gemstones.
Refractive Index / Birefringence :

1.642 – 1.646 / 0.002 – 0.006. Range: 1.637 – 1.651

Simulants (with 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.
Sources :

Sri Lanka, Myanmar, Norway, Canada, India, Germany, Pakistan, Madagascar, Tanzania, Brazil.

Specific Tests :
  • Attacked by hydrochloric and sulphuric acid.
  • Reacts to heat and may lose color.
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.

Synthesis :

Synthesized for use in lasers but cut synthetics are not sold commercially.

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