The most common source of fluoride (F-) in the environment is the natural mineral fluorapatite, which is a fluorinated calcium phosphate rock. Fluorapatite is mined as the primary source of phosphate fertilizer.
Ref: Fluoride Fact Sheet. U.S. Department of the Interior. Revision Date 9/21/01.

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The following is from: PHOSPHATIC FERTILISER MANUFACTURE IN AUSTRALIA

Rock phosphate is not a pure chemical, the chief component is Fluorapatite bearing the chemical formula: 3 Ca3(PO4)2CaF2 or Ca10(PO4)6F2

Superphosphate Manufacture:
... The composition of most phosphatic rocks varies considerably but generally they can be represented by the simplified formula: Ca(PO4) CaX where X is generally Fluorine F2
... When reactive silica is present in the rock, it liberates much greater quantities of fluorine in the form of SIF4 which reacts with water to form Hydrofluosilicic acid H2SiF6.
The resulting hydrofluosilicic acid may be recycled in the gas scrubber until it reaches a concentration of approximately 20%. This solution may then be utilised in the production of by-products such as aluminium fluoride (Aluminium industry) or as a source of fluorine in the Water Supply Fluidisation [fluoridation] program.

Single superphosphate is produced by mixing ground phosphate rock with sulfuric acid and water to produce a solid product under controlled conditions of residence time and temperature. The technolofy consists of phosphate rock grinding, reaction (denning), drying, maturing and fluorine scrubbing.

Adverse Effects:

Atrophic rhinitis
Lung
Contamination Incident: Placentia Bay, Newfoundland (1969)

Environmental:
• Abnormally high fluoride values were found in the phosphate-polluted sediments in the Jordan Gulf of Aqaba (Red Sea).
• Nuaru: intensive phosphate mining during the past 90 years has left the central 90% of Nauru a wasteland and threatens limited remaining land resources

Yes Inert 
(cited by EPA in April 28, 2004, Federal Register)

CFR 180.920
(new: April 28, 2004)

(Ca5F(PO4)3)
Fluoroapatite
Phosphate rock

See also
• The Phosphate Fertilizer Industry: An Environmental Overview
• Abstracts on Phosphate Fertilizers that cite effects or levels of fluoride

About: Apatite is a member of the Apatite group, a group of isomorphous hexagonal minerals. Apatite may be regarded as a single mineral, but is usually divided into three more minerals: Fluorapatite, Chlorapatite, and Hydroxylapatite. Since it is hard to distinguish between these minerals, and since they may partially replace each other, a distinction between them is rarely made, and they are simply called "Apatite". However, most Apatite is Fluorapatite, the most common member by far.

Apatite is the most common phosphate mineral, and is the main source of the phosphorus required by plants. The bones and teeth of most animals, including humans, are of the same material as Apatite.

Apatite is named from the Greek word apate, which means "deceit", since Apatite has a similar appearance to so many minerals.

Uses: Apatite is the main source of phosphorus. Phosphorus was previously extracted from crystalline Apatite, but nowadays is extracted from enormous deposits of Apatite-rich rock. Apatite is essential in the manufacture of phosphate fertilizers, and is very important in the chemical and pharmaceutical industries. Apatite is also a popular collectors mineral, and some transparent specimens are faceted for collectors.

Noteworthy Localities: Apatite is a common mineral, and fine localities are worldwide. Enormous deposits are in the Kola Peninsula, Russia, containing both crystals and botryoidal material. Some of the finest crystals came from Ehrenfriedersdorf, Saxony Germany, where they are blue to purple in color. Colorless, hexagonal crystals were found in the Tyrol, Austria, and excellent material from Panasqueira, Portugal. Deep blue crystals are found in Campo Formosa, Bahia, Brazil, and in Sri Lanka. Enormous deposits mined for industrial use exist in Nauru [see box below], Morocco, Algeria, Tunisia, Egypt, and Israel ...

Ref: http://www.minerals.net/mineral/phosphat/apatite/apatite.htm

Note from EC: The fluoride concentration in the Nauru phosphate deposits has been estimated at 3.0%. • Nauru - this map and description is from "CIA - The World Factbook" website for Nauru. Background: Nauru's phosphate deposits began to be mined early in the 20th century by a German-British consortium; the island was occupied by Australian forces in World War I. Nauru achieved independence in 1968 and joined the UN in 1999. Nauru is the world's smallest independent republic. Location: Oceania, island in the South Pacific Ocean, south of the Marshall Islands Area - comparative: about 0.1 times the size of Washington, DC Population: 12,809 (July 2004 est.) Infant mortality rate: total: 10.14 deaths/1,000 live births male: 12.76 deaths/1,000 live births female: 7.39 deaths/1,000 live births (2004 est.) Economy - overview: Revenues of this tiny island have traditionally come from exports of phosphates, but reserves are now depleted. Few other resources exist with most necessities being imported, mainly from Australia, its former occupier and later major source of support. The rehabilitation of mined land and the replacement of income from phosphates are serious long-term problems...

Environment - current issues: limited natural fresh water resources, roof storage tanks collect rainwater, but mostly dependent on a single, aging desalination plant; intensive phosphate mining during the past 90 years - mainly by a UK, Australia, and NZ consortium - has left the central 90% of Nauru a wasteland and threatens limited remaining land resources Geography - note: Nauru is one of the three great phosphate rock islands in the Pacific Ocean - the others are Banaba (Ocean Island) in Kiribati and Makatea in French Polynesia; only 53 km south of Equator