|Optic nature||Uniaxial -|
Apatite occurs in yellow, green, violet, purple, blue, brown, colorless and pink and can be transparent to translucent.
DR, Uniaxial negative
Refractometer readings are in the range of tourmaline, topaz, andalusite and danburite but usually with a very low birefringence of 0.003.
Full range: nω = 1.629 - 1.667 and nε = 1.624 - 1.666 with a full birefringence of 0.001-0.007.
The spectroscope is a good diagnostic tool in seperating apatite from gemstones as tourmaline and topaz.
Blue apatite will, usually, show a rare earth spectrum line in the blue (praseodymium).
Blue-green stones may have added spectrum lines in the yellow (didymium) and line(s) in the green (praseodymium).
Yellow gems show the rare earth spectrum of greenish-blue without the line in the blue.
Neon blue stones may show rare earth spectra in the yellow.
- Blue: Blue to light blue (LW and SW)
- Yellow: Purplish Pink (stronger in LW)
- Green: Greenish-yellow (stronger in LW)
- Violet: Greenish-yellow (LW);Light purple (SW)
Chelsea Colour Filter
Green-blue stones: green
Apatite has weak pleochroism, so this tool may not be very useful except for blue stones where the dichroism is more profound (blue and pale yellow).
A nice uniaxial negative interference figure should be found.
Brazil, Burma, Mexico
Violet and Purple are found in Maine and Afghanistan.
Clouds of tiny white crystal inclusions may be easily observed.
G&G Articles on Apatite 1934-1980
- Summer 1962, Cat's-eye apatite, p. 315, 2pp.
- Summer 1963, Yellow cat's-eye apatite, p. 44, 1p.
- Winter 1965, Cat's-eye apatite, p. 372, 1p.
- Summer 1966, A cat's-eye apatite of 220 cts., p. 46, 1p.
- Winter 1972, Rare Earth Absorption Spectra in Apatite, by Anderson, p. 101, 1p.
- Winter 1972, A 40 ct. cat's-eye apatite, p. 114, 1p.
- A Students' Guide to Spectroscopy (2003) - Colin Winter FGA, DGA ISBN 0954485300
- Introduction to Optical Mineralogy 3rd edition (2003), Prof. W.D. Nesse