Francolite

Francolite is a carbonate rich variety of the mineral fluorapatite[1] and is present in most sedimentary phosphorites. It has a variable chemical composition which can be represented by (Ca,Mg,Sr,Na)10(PO4,SO4,CO3)6F2−3.[2] The mineral was named after its occurrence at Wheal Franco, Whitchurch, Tavistock District, Devon, England.[1]

References

  1. ↑ 1.0 1.1 http://www.mindat.org/min-4910.html Mindat.org
  2. ↑ 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, 1983