Francolite is a carbonate rich variety of the mineral

fluorapatite Fluorapatite, often with the alternate spelling of fluoroapatite, is a phosphate mineral with the formula Ca5(PO4)3F (calcium fluorophosphate). Fluorapatite is a hard crystalline solid. Although samples can have various color (green, brown, bl ...

http://www.mindat.org/min-4910.html Mindat.org and is present in most

sedimentary Sedimentary rocks are types of rock (geology), rock that are formed by the accumulation or deposition of mineral or organic matter, organic particles at Earth#Surface, Earth's surface, followed by cementation (geology), cementation. Sedimentati ...

phosphorite Phosphorite, phosphate rock or rock phosphate is a non-detrital sedimentary rock that contains high amounts of phosphate minerals. The phosphate content of phosphorite (or grade of phosphate rock) varies greatly, from 4% to 20% phosphorus pentoxi ...

s. It has a variable chemical composition which can be represented by .R. A. Benmore, M. L. Coleman, and J. M. McArthur, Origin of is sedimentary francolite from its sulphur and carbon isotope composition. Nature 302: 516, 198

/ref> The mineral was named after its occurrence at

Wheal Franco Wheal may refer to: * Wheals, a type of skin lesion * Brad Wheal (born 1996), British cricketer * Donald James Wheal (1931–2008), British British television writer, novelist and non-fiction writer * David John Wheal, Australian businessman * "Th ...

, Whitchurch, Tavistock District,

Devon, England Devon ( , historically known as Devonshire , ) is a ceremonial and non-metropolitan county in South West England. The most populous settlement in Devon is the city of Plymouth, followed by Devon's county town, the city of Exeter. Devon i ...

References

Phosphate minerals {{phosphate-mineral-stub