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Fluoborite found in Italy
CategoryBorate mineral
(repeating unit)
IMA symbolFbo[1]
Strunz classification6.AB.50
Crystal systemHexagonal
Crystal classDipyramidal (6/m)
H-M symbol: (6/m)
Space groupP63/m
Unit cella = 8.8612, c = 3.1021 [Å]; Z = 3
Formula mass186.61 g/mol
ColorColorless to violet or white
Crystal habitAcicular, prismatic, stellate
CleavageGood on {0001}
Mohs scale hardness3.5
LusterVitreous to silky
DiaphaneityTranslucent to transparent
Specific gravity2.98
Optical propertiesUniaxial (-)
Refractive indexnω = 1.570 nε = 1.534
Ultraviolet fluorescenceIntense cream-white under SW UV

Fluoborite has a chemical formula of Mg3(BO3)(F,OH)3. Its name comes from its main chemical components, FLUOrine and BORon. It was first described in 1926.[3]

Fluoborite's crystal system is hexagonal, meaning it has one six-fold axis of rotation. It also has a mirror plane perpendicular to the c-axis.[5] Fluoborite is uniaxial, just like all other hexagonal minerals. Uniaxial means it has only one optic axis. It is anisotropic. Its relief is low, and it is birefringent.

There are three major settings fluoborite is found. It is found in skarns developed in metamorphosed boron-rich magnesium rocks, contact metamorphosed marble, and in contact metasomatic magnetite deposits. There are two major type localities for fluoborite. One is Tall Mine, Kallmora, Norberg, Västmanland, Sweden. It is an iron mine in a contact metasomatic magnetite deposit. The other type locality is the Huerta del Vinagre mine, Spain.[6]

It occurs associated with ludwigite, chondrodite, magnetite and calcite in the Tallgruvan, Sweden occurrence. It occurs with mooreite, willemite, fluorite, hydrozincite, pyrochroite, zincite and rhodochrosite at Sterling Hill, New Jersey.[2]


  1. ^ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
  2. ^ a b Handbook of Mineralogy
  3. ^ a b Fluoborite on Mindat.org
  4. ^ Fluoborite Mineral Data on Webmineral
  5. ^ Anthony, J.W., Bideaux, R.A., Bladh, K.W., and Nichols, M.C. (2003)Fluoborite. Handbook of Mineralogy Volume V Borates, Carbonates, Sulfates, 791 p. Mineral Data Publishing, Tucson, AZ.
  6. ^ Camara, F. and Ottolini, L., 2000. "New data on the crystal-chemistry of fluoborite by means of SREF, SIMS, and EMP analysis." http://rruff.geo.arizona.edu/doclib/am/vol85/AM85_103.pdf. Accessed 1 November 2010.