Francolite
Image: No machine-readable author provided. Kluka assumed (based on copyright claims). (CC BY-SA 3.0)
Mineral NameFrancolite
Chemical FormulaCa₅(PO₄,CO₃)₃(F,OH)
Mohs Hardness5
Crystal Systemhexagonal
Streak Colorwhite
Cleavageimperfect basal {0001}
Fractureconchoidal to uneven
Specific Gravity3.1
Colorslight blue-green, green, brown, gray
Transparencytranslucent to opaque
Type LocalityKola Peninsula, Russia
Mineral GroupPhosphates
Usessource of phosphorus (as phosphorite), collector specimens
Associated Mineralsquartz, calcite, chert, clay minerals
Raritycommon
Description
This specimen displays a beautiful light blue-green botryoidal habit, forming a bubbly, mammillary crust over a darker, possibly brownish matrix.
Geological Context
Francolite is a carbonate-fluorapatite, a common variety of apatite, often found as a primary component of sedimentary phosphorite deposits or as a secondary mineral in various rock types, including igneous and metamorphic rocks.
