Apatite

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Apatite is a very common mineral but transparent gemstone-quality is extremely rare. Despite the fact that is the defining mineral for 5 on Mohs scale of hardness, the gemstone remains virtually unknown to most, and is seldom found in jewelry stores. However, because apatite occurs in such a wide variety of attractive colors and forms, it is a favorite among gemstone collectors. The name ‘apatite’ was derived from a Greek word meaning ‘cheat’. It was given its name because of its close resemblance to several other gemstones that are often more valuable.

It is a group of phosphate minerals, usually referring to hydroxylapatite, fluorapatite and chlorapatite

• Hydroxylapatite
• Fluorapatite
• Chlorapatite

Apatite Physical Properties

• It is best known for its use as an index mineral with a hardness of 5 in the Mohs Hardness Scale. It is usually green in color, but can be yellow, brown, blue, purple, pink, or colorless.
• These colors are often so vivid that it has frequently been cut as a gemstone.
• It is a brittle material. It breaks by both fracture and cleavage, but the cleavage is generally indistinct. Hexagonal apatite crystals are sometimes found in igneous and metamorphic rocks.

Apatite Optical Properties

Colour– Colourless

Pleochroism – Non pleochroic

Birefringence – First order grey

Interference Figure – Uniaxial negative

Form –Small euhedral to subhedral elongate prismatic crystals with hexagonal cross sections

Cleavage – Poor

Twinning – Rare

Optic Orientation – parallel extinction

Distinguishing Features – moderate to high relief, low birefringence and uniaxial character

Geologic Occurrence

• Apatite forms under a wide variety of conditions and is found in igneous, metamorphic, and sedimentary rocks.
• The most important deposits of apatite are in sedimentary rocks formed in marine and lacustrine environments. There, phosphatic organic debris had accumulated and was mineralized during diagenesis.
• As a mineral, apatite is chiefly used as a phosphorus source for the manufacture of fertilizers.
• One of the primary physical properties of apatite is that, in its mineral form, apatite is very stable and does not easily dissolve in a natural environment. In their mineral forms, all apatite have the ability to absorb radioactive and metallic contaminants, and keep them locked. This is one of the most significant apatite properties which makes it an excellent choice for removing radioactive contaminants, like Strontium-90, from groundwater.
• It can also be used as an ore mineral for rare earth metals such as Scandium, Yttrium and the Lanthanides
• It is occasionally used as a gemstone. Green and blue varieties, in finely divided form, are pigments with excellent covering power.
• During digestion of apatite with sulfuric acid to make phosphoric acid, hydrogen fluoride is produced as a byproduct from any fluorapatite content. This byproduct is a minor industrial source of hydrofluoric acid.
• They are also a proposed host material for storage of nuclear waste, along with other phosphates.

Sources

• Brazil, Canada, India, Madagascar, and Mexico produce most gem-quality apatites. Notable gem-quality sources, organized by color:
• Blue: Brazil, Myanmar; Sri Lanka.
• Blue-green: Madagascar (neon blue-green); Arendal, Norway
• Violet: Germany; Portugal; Maine, California, United States.
• Yellow: Brazil; Canada; Durango, Mexico; Murcia, Spain.
• Green: Canada (trade name, Trilliumite); India; Kenya; Madagascar; Mozambique; Myanmar; Portugal; Spain.
• Brown: Canada.
• Colorless: Germany; Italy; Myanmar.

Phosphate Rock

Phosphate rock and phosphorite are names used for sedimentary rocks that contain at least 15% to 20% phosphate on the basis of weight. The phosphorous content in these rocks is mainly derived from the presence of apatite minerals

Uses of Apatite as Phosphate Rock

• Most of the phosphate rock mined throughout the world is used to produce phosphate fertilizer. It is also used to produce animal feed supplements, phosphoric acid, elemental phosphorous, and phosphate compounds for the chemical industry.
• China is the largest producer of phosphate rock, producing approximately 100 million tons in 2014. The United States, Russia, Morocco, and Western Sahara are also major phosphate producers.
• Over 75% of the world’s reserves of phosphate rock are located in Morocco and Western Sahara.

References

• Hobart M. King (2018) Apatite, Phosphorite and Phosphate Rock https://geology.com/minerals/apatite.shtml
• Market Price , https://roughmarket.com/apatite/
• Arem,J,E.,Smigel,B (2018) Apatite Value, Price, and Jewelry Information, International Gem Society
• Villalba,G.,Ayres, R,U.,Schroder, H(2008). “Accounting for Fluorine: Production, Use, and Loss”. Journal of Industrial Ecology.
• USGS, Mineral commodity summaries, Available at http://minerals. usgs.gov/minerals/pubs/commodity/phosphate_rock/index.html#mcs verified 19 April 2013).