Francolite is a carbonate rich variety of the mineral Fluorapatite 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. The mineral was named after its occurrence at Wheal Franco, Whitchurch, Tavistock District, Devon, England.