Formula: Ca5(PO4)3(F,OH, Cl)3
Ca often replaced by Sr, Mn.
Also contains: Ce, rare earths, U, Th.
PO4 replaced by SO4 + SiO2.
Carbonate apatites contain CO2. F is also present in the variety of francolite.
CRYSTALLOGRAPHY Hexagonal. Crystals usually prismatic or stubby; massive, granular, compact; oolitic, earthy.
COLORS: Colorless, green, white, blue, brown, yellow, purple, violet, gray, pink, and various shades of most of these colors.
LUSTER: Vitreous in crystals
REFRACTIVE INDEX 1.632 – 1.42, (variable with composition)
HARDNESS 5 (some massive varieties 3-4).
SPECIFIC GRAVITY 3.10 – 3.35
DENSITY 3.10-3.35 (massive varieties 2.5 -2.9)
CLEAVAGE Poor. Fracture conchoidal to uneven. Brittle
HEAT SENSITIVE Yes, very.
WEARABILITY* Very Good
SPECIAL CARE INSTRUCTIONS Avoid rough handling
*Wearability is graded as Excellent, Very Good, Good, Poor, and Forget It! For more details see the article on “Hardness and Wearability.”
Optics: e= 1.598 -1.666; o = 1.603 1.667. Very variable with composition.
Gem varieties: o = 1.632 -1.649, e= 1.628-1.642.
Uniaxial (-); francolite may be biaxial, 2V = 25 – 40°.
Chlorapatites have the lowest birefringence (~0.001); fluorapatites medium (0.004); hydroxylapatites higher (0.007); carbonate apatites as high as 0.008; and francolite as high as 0.013.
|Hydroxylapatite||Holy Springs, Georgia||-||1.651||1.644||0.007||3.21|
|Hydroxylapatite||Sweden (with Mn)||blue-green||1.646||1.641||0.005||3.22|
|Carbonate apatite with Fluorine||Devonshire, England (francolite)||-||1.629||1.624||0.005||3.14|
|Carbonate apatite||St Paul’s Rocks, Atlantic Ocean||-||1.603||1.598||0.005||-|
|Cut gemstone||Kenya||dark green||1.641||1.637||0.004||-|
|Cut gemstone||Madagascar||dark green||1.637||1.632||0.005||-|
|Cut gemstone||Brazil||deep blue||1.638||1.632||0.006||-|
|Cut gemstone||Sri Lanka (catseye)||brown||1.647-||1.640-||0.007||-|
|Cut gemstone||Tanzania (catseye)||yellow||1.636-||1.632-||0.004||3.22-|
Pleochroism: Distinct in blue-green varieties; otherwise weak. Yellow stones may give yellowish/greenish or brownish/greenish.
Gem blue apatite shows strong dichroism: blue/yellow.
Spectral: Blue and yellow apatites display a rare earth (“didymium,” i.e. praseodymium + neodymium) spectrum. Yellow gems have 7-line group at 5800 and 5 lines at 5200. Blue gems give broad bands at 5120, 4910, and 4640.
Luminescence: Yellow gems fluoresce lilac-pink in SW and LW (stronger in LW). Blue apatite fluoresces violet-blue to sky blue, and violet material fluoresces greenish-yellow (LW) or pale mauve (SW). Green apatite fluoresces a greenish mustard color, LW stronger than SW. Manganapatite fluoresces pink in SW.
Occurrence:Apatite is found in a wide variety of rock types. Igneous rocks are usually characterized by F and OH varieties, some containing Mn. Apatite occurs in pegmatites, hydrothermal veins and cavities, metamorphic rocks, and as detrital grains in sedimentary rocks and phosphate beds.
Blue: Burma; Sri Lanka; Brazil.
Blue-green: Arendal, Norway, (variety called moroxite); also: Gravelotte, East Transvaal, South Africa.
Violet: Germany; Maine; California
Yellow: Durango, Mexico, Murcia, Spain; Canada; Brazil.
Green: India; Canada (trade-named Trilliumite); Mozambique; Madagascar; Spain; Burma.
Colorless: Burma; Italy; Germany
Catseye: Blue green and green from Sri Lanka and Burma.
Green catseyes also occur in Brazil, and yellow stones in Sri Lanka and Tanzania
Stone Sizes: Cut apatities are not common in museum collections. Blue gems (Brazil) are almost always small (1-2 carats). Burma produces 10 carat blue gems, but this color is very scarce in larger sizes. Yellow gems up to 15-20 carats are known from Mexico, but larger ones are quite rare. Violet stones are the rarest and smallest in general, usually under 2 carats. However, the Roebling purple apatite in SI is ~100 grams, a superb crystal. Blue-green clean stones are usually less than 5 carats, rare if larger. Green apatite occurs in large crystals; Canadian material has yielded 100 carat flawless stones. The world’s largest golden green gem may be a 147 carat stone from Kenya. Yellowish catseyes range up to about 15 carats and green catseyes a bit larger (20 carats).
Comments: Fluorapatite is the commonest apatite variety. Apatite is abundant throughout the world, and is, in fact, the main constituent of bones and teeth. It is also the most abundant phosphorus-bearing mineral, especially cellophane, the massive type that makes up large beds in some localities. Apatite is brittle and heat sensitive, and must be cut and worn with care. Property cut stones are truly magnificent, however, since they are both bright and richly colored. It is possible to assemble suites of as many as 20 gems, all different colors.
Mexican yellow apatite is perhaps the most abundant material available, and thousands of crystals exist that would cut stones up to 5 carats. Larger pieces are rare, however, even from this locality. The Mexican material may be turned colorless by careful heating.
The catseye in Tanzanian stones may be so intense that the material resembles catseye Chrysoberyl.
Lazurapatite is a mixture of lapis and apatite that is found in Siberia.
Names: From the Greek, meaning to deceive because mineralogists had confused apatite with the other species.
Apatite, a stone seldom found in jewelry stores and virtually unknown to the general public, is beloved by collectors for its many different colors and forms. Only with the recent availability of the neon blue-green variety from Madagascar, has its jewelry use increased. The color of the best specimens of this type rivals the famed Paraiba tourmalines, but alas, this gem lacks their toughness and hardness. At 5 on the Mohs scale, apatite must be cut, set, and worn gently. Earrings, pendants, pins, and tie tacks are probably safe, but ring use should be limited to occasional wear pieces with protective settings. Care for this stone is similar to that given opals, it is heat and shock sensitive, so steamers and ultrasonics must be avoided.
Gems are available in yellows and various shades of blues and greens. Some of the blues show chatoyancy and can be cut as cat’s eyes. Main sources are Brazil, Canada, India, Mozambique, and Madagascar.
The major sources listing values for gems do not yet catalog the blue-green variety so I have extrapolated from the data available on the other colors. Sinkankas lists fine blue stones of between .5 to 1.5 ct at $75 to $200 per carat. His estimate for blue Brazilian stones is $100/ct. The rarest of all varieties, a rich purple from Maine, tops the list at $250 per carat.
The degree of polish can vary on this soft stone due to skill levels of individual cutters, giving well polished stones premium value. As with most gems, saturation of color, size, and clarity are the major determiners of value. Text and photos courtesy of Barbara Smigel at Artistic Colored Stones.
The IGS gratefully acknowledges Dr. Joel Arem, author of the now out-of-print Color Encyclopedia of Gemstones, for allowing us to reproduce some of his content above with attribution.