Apatite is a calcium phosphate mineral that produces bright blue, green, yellow and violet gemstones. The best-known gem material today is the neon blue to blue-green apatite from Madagascar. Apatite is soft for a gem, at 5 on the Mohs scale, so it needs more care than most jewelry stones. It is also the reference mineral for hardness 5 on that scale.
What apatite is
Apatite is the name of a group of phosphate minerals. Most gem apatite is fluorapatite, in which fluorine sits in the crystal structure. Chlorapatite and hydroxylapatite are related members. The group sits in the phosphate class of minerals, a category described on the page about how minerals are classified.
The name comes from the Greek word apatein, "to deceive." Early mineralogists often mistook apatite crystals for other minerals such as beryl, tourmaline, peridot and olivine. The confusion still happens with cut stones, because apatite comes in many colors and its refractive index falls between those of several common gems.
Apatite is everywhere in the Earth's crust. Most of it is massive or fine-grained and of no use as a gem. Phosphate rock rich in apatite is mined for fertilizer, and hydroxylapatite is the main mineral in tooth enamel and bone. Gem-quality crystals are much rarer: they need to be large, clear and well colored.
Colors of apatite
Trace elements and small changes in chemistry give apatite a wide color range.
Neon blue apatite
Madagascar produces bright blue to greenish blue apatite in quantity. Its saturated color invites comparison with Paraiba tourmaline, though the two are unrelated and apatite is far softer and less costly. Brazil also produces blue apatite. Our page on the gems of Madagascar covers the island's other gem deposits.
Yellow and green apatite
Yellow-green apatite was once called "asparagus stone" in the trade. The classic source of yellow crystals is Cerro de Mercado near Durango, Mexico, an iron-ore deposit known for sharp, transparent yellow apatite. Green apatite comes from several countries, including Brazil and Madagascar.
Violet and pink apatite
Violet apatite is rare. Fine purple crystals have come from Maine in the United States and from Germany. These are mainly collector pieces.
Cat's eye apatite
Apatite with dense parallel inclusions can be cut as a cabochon to show a sharp eye. Cat's eye apatite comes in green, blue and yellow, mainly from Sri Lanka and Brazil. It can look like cat's eye chrysoberyl, but chrysoberyl is much harder and denser.
Apatite and the Mohs scale
Friedrich Mohs chose apatite as the reference mineral for hardness 5 when he devised his scale in 1812. Apatite sits between fluorite (4) and orthoclase feldspar (6). A steel knife blade is roughly 5.5, so a knife can just scratch apatite, which helps with a field test on rough crystals. The Mohs hardness scale page explains why the scale ranks minerals without measuring equal steps between them.
For jewelry, hardness 5 matters a great deal. Ordinary dust contains quartz, which is hardness 7. Over time, wiping or brushing against quartz particles will scratch and dull an apatite surface. Facet edges round off and the polish loses its brightness, especially on a ring.
Identifying apatite
Gemologists use a few tests to separate apatite from look-alikes.
- The refractive index is about 1.63 to 1.65, with low birefringence, measured on a standard refractometer.
- The specific gravity is about 3.2.
- Yellow apatite often shows a sharp set of absorption lines in the yellow part of the spectrum, caused by rare earth elements. This "rare earth spectrum" is a classic identifying feature seen in a handheld spectroscope.
- Apatite is brittle and often shows small fractures and liquid inclusions under magnification.
The tools behind these tests are described on our page about gemological instruments. Blue apatite can resemble tourmaline, topaz or glass, but its lower hardness and its readings usually settle the question.
Treatments
Most apatite is sold untreated. Some material may be heated to lighten or change color, but treatment is not widespread. Ask the seller, and expect a lab report only for larger or unusually fine stones.
Wearing and caring for apatite
Apatite is a good choice for earrings, pendants and brooches, where it avoids most knocks and abrasion. In a ring, choose a protective setting and plan for occasional wear only. Bezel settings guard the girdle better than prongs, as explained on the gemstone settings page.
Apatite is sensitive to more than scratches:
- It is brittle and can chip if struck against a hard surface.
- Acids attack it, including some household cleaners and even prolonged contact with acidic substances.
- Sudden temperature changes can crack it.
Clean apatite with lukewarm soapy water and a soft cloth. Do not use ultrasonic or steam cleaners. Store it apart from harder gems, which will scratch it. For a wider view of how hardness, toughness and stability combine, see gemstone durability, and for cleaning methods by gem type see how to clean jewelry safely.
Buying apatite
Color is the main value factor. Saturated neon blue and blue-green stones are the most popular, followed by bright yellow and green. Eye-clean stones command more than included ones, since apatite's color is easy to see in a faceted stone and inclusions are distracting. Large clean stones exist, but blue Madagascar apatite above a few carats is less common.
Because apatite is soft, check facet edges and the table for scratches or chips, especially on stones that have been set before.
Frequently asked questions
Is apatite a durable gemstone?
Apatite is fairly soft at Mohs 5 and is brittle, so it scratches and chips more easily than most jewelry gems. It suits earrings and pendants better than everyday rings.
Is apatite the same as Paraiba tourmaline?
No. Neon blue apatite can look similar in color, but apatite is a phosphate mineral and Paraiba tourmaline is a copper-bearing tourmaline. Their refractive index, hardness and price are different.
Why is apatite on the Mohs scale?
Friedrich Mohs picked apatite as the standard for hardness 5 because it was common and consistent in hardness. Minerals that scratch apatite are harder than 5.
Where does apatite come from?
Gem apatite comes mainly from Madagascar, Brazil, Mexico, Sri Lanka and Myanmar, with collector crystals from Canada, Maine and Germany.