Although too brittle for most jewelry use, properly cut apatite gems are truly magnificent. A collector could assemble a suite of as many as twenty of these bright gems, all with different colors.
Apatite
Value
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Blue Brazilian apatites and those with a “neon” blue-green color, similar to that of Paraíba tourmalines, command the highest prices. Rare, rich purple specimens from Maine are also highly prized.
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.
Chatoyancy. (Synthetics may show color change; natural apatites do not).
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 francolite.
Distinct in blue-green varieties; otherwise weak. Yellow stones may give yellowish/greenish or brownish/greenish.
Gem blue apatite shows strong dichroism: blue/yellow.
Very variable with composition:e = 1.598-1.666; o = 1.603-1.667. Gem varieties: o = 1.632-1.649, e = 1.628-1.642. See "Apatite Properties and Identification" below. Uniaxial (-); francolite may be biaxial, 2V = 25-40°.
Optic Sign
Uniaxial -, Biaxial -
Etymology
From the Greek apatein, meaning “to deceive,” because mineralogists had confused apatite with other species.
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.
The apatite mineral group occurs abundantly throughout the world. In fact, bones and teeth consist mainly of a variety known as hydroxylapatite. As collophane, a massive cryptocrystalline variety that occurs in some localities as large beds, apatite also serves as the most abundant phosphorus-bearing mineral.
Most of the gemstones referred to as apatite are of the commonest variety, fluorapatite. Other gem-quality apatites include the aforementioned hydroxylapatite as well as carbonate-rich apatite, mimetite, moroxite, vanadinite, wilkeite, and the rare chlorapatite.
Lazurapatite, a mixture of lapis lazuli and apatite, occurs in Siberia.
Strictly speaking mineralogically, the term “apatite” refers to the mineral group only. Individual varieties should be referred to by their specific names. However, you’ll frequently find many gemstones described and sold as just “apatites,” without further classification.
Does Apatite Make a Good Jewelry Stone?
Prior to the discovery of the now coveted neon blue-green apatites in Madagascar, these colorful but little-known gemstones seldom found their way into jewelry collections. Nevertheless, mineral collectors prized them not only for their colors but also their beautiful fluorescence.
Since the Madagascar finds, the jewelry use of apatites of all colors has increased. Although the color of the best neon-blue green specimens can approximate that of the storied Paraíba tourmalines, all gem-quality apatites have a hardness of 5 at best. Unfortunately, apatites don’t have the toughness of their tourmaline rivals. As jewelry stones, they will require special care.
Notable Apatite Colors and Varieties
In addition to prized blue-greens and purples, apatites can occur in other beautiful colors.
Mexican Yellow Apatite
Mexican yellow apatite is perhaps the most abundant gem material available. Thousands of crystals exist that would cut stones up to five carats.
Chatoyancy can occur in blue-green and green gems from Myanmar and Sri Lanka. Brazil can produce green cat’s eyes. Sri Lanka and Tanzania can produce yellow cat’s eyes. The chatoyancy in Tanzanian apatites can be so intense that the material resembles cat’s eye chrysoberyl.
Light green apatites are sometimes referred to by the trade name “asparagus stones.”
Apatite Properties and Identification
Distinguishing Apatite and Tourmaline
Aside from a destructive scratch test to determine hardness, distinguishing faceted apatites from tourmalines can sometimes prove challenging. Many of their properties overlap. Read this article on difficult separations for tips on identifying these gems.
Apatite Properties by Variety and Locality
Variety
Locality
Color
o
e
Birefringence
SG
Chlorapatite
Japan
yellow
1.658
1.653
0.005
–
Hydroxylapatite
Holy Springs, Georgia
–
1.651
1.644
0.007
3.21
Fluorapatite
Finland
blue-green
1.633
1.629
0.004
3.2
Hydroxylapatite
Sweden (with Mn)
blue-green
1.646
1.641
0.005
3.22
Fluorapatite
Sweden
colorless
1.634
1.631
0.003
3.27
Carbonate apatite with Fluorine
Devonshire, England (francolite)
–
1.629
1.624
0.005
3.14
Hydroxylapatite
Mexico
yellow
1.634
1.630
0.004
–
Fluorapatite
Canada
green
1.632
1.629
0.003
–
Fluorapatite
Maine
purple
1.633
1.630
0.003
–
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
Zimbabwe
yellow-green
1.643
1.638
0.005
–
Cut gemstone
Mexico
yellow
1.637
1.633
0.004
–
Cut gemstone
Madagascar
dark green
1.637
1.632
0.005
–
Cut gemstone
Myanmar
green
1.636
1.632
0.004
–
Cut gemstone
Brazil
deep blue
1.638
1.632
0.006
–
Cut gemstone
Canada
green
1.632
1.628
0.004
–
Cut gemstone
Sri Lanka (cat’s eye)
brown
1.647-1.649
1.640-1.642
0.007
–
Cut gemstone
Tanzania (cat’s eye)
yellow
1.636-1.640
1.632-1.637
0.004
3.22-3.35
Birefringence
Chlorapatites have the lowest birefringence (~0.001).
Fluorapatites: 0.004.
Hydroxylapatites: 0.007.
Carbonate apatites can range as high as 0.008. (The francolite variety can even reach 0.013).
Blue gems (Brazil) almost always range on the small side (1-2 carats). Myanmar produces 10-carat blue gems. However, this color is very scarce in larger sizes.
Yellow gems from Mexico up to 15-20 carats are known, but larger ones are quite rare.
The rarest and smallest in general, violet stones usually fall under 2 carats. However, the Roebling purple apatite in the Smithsonian Institution weighs approximately 100 grams (500 carats), a superb crystal.
Blue-green clean stones usually weigh less than 5 carats, very rarely more.
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 cat’s eyes range up to about 15 carats, while green cat’s eyes can weigh a bit larger (20 carats).
Caring for Apatite Jewelry
Brittle and sensitive, apatites must be cut and worn gently. Although difficult to cut and polish, apatites faceted with gem designs for quartz, tourmaline, and topaz will look wonderful.