Chemistry:Falsterite

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Falsterite
General
CategoryPhosphate mineral
Formula
(repeating unit)
Ca2MgMn2+2(Fe2+0.5Fe3+0.5)4
Zn4(PO4)8(OH)4(H2O)14
Crystal systemMonoclinic
Crystal classPrismatic (2/m)
(same H-M symbol)
Space groupP21/c
Unit cella = 6.39, b = 21.26
c = 15.37 [Å]; β = 90.56° (approximated); Z = 2
Identification
ColorGreenish-blue
Crystal habitthin plates, rectangular laths
Cleavage{010}, perfect
FractureUneven
|re|er}}Vitreous
StreakVery pale greenish-blue
DiaphaneityTransparent
Density2.78 (measured); 2.84 (calculated; approximated)
Optical propertiesBiaxal (-)
Refractive indexnα=1.58, nβ=1.60, nγ=1.61 (approximated)
PleochroismColorless to very pale yellow (X & Z), blue-green (Y)
DispersionStrong
References[1][2]

Falsterite is a rare phosphate mineral[2] with the formula Ca2MgMn2+2(Fe2+0.5Fe3+0.5)4Zn4(PO4)8(OH)4(H2O)14.[1] It is a pegmatitic mineral, related to the currently approved mineral ferraioloite.[2]

Occurrence and association

Falsterite was found in Palermo No. 1 pegmatite, North Groton, Grafton County, New Hampshire, US. Co-type locality is pegmatite at Estes quarry, Baldwin, Cumberland County, Maine, US. Falsterite is a product of alteration of triphylite and sphalerite.[1]

Crystal structure

Main features of the crystal structure of falsterite, which is somewhat similar to that of schoonerite, are:

  • chains of Fen+O6 octahedra, displaying edge-sharing
  • chains of ZnO4 tetrahedra, that display corner-sharing
  • sheets, parallel to {010}, formed by linking the above two types of chains by PO4 tetrahedra
  • slabs formed by linking the sheets with MnO6 octahedra and CaO7 polyhedra

The slabs are bridged by dimers of MgO6 octahedra that display edge-sharing. Magnesium-bearing octahedra share edges with zinc-bearing tetrahedra.[1]

References

  1. 1.0 1.1 1.2 1.3 Kampf, A.R., Mills, S.J., Simmons, W.B., Nizamoff, J.W., and Whitmore, R.W., 2012. Falsterite, Ca2MgMn2+2(Fe2+0.5Fe3+0.5)4Zn4(PO4)8(OH)4(H2O)14, a new secondary phosphate mineral from the Palermo No. 1 pegmatite, North Groton, New Hampshire. American Mineralogist 97(4), 496-502
  2. 2.0 2.1 2.2 "Falsterite: Falsterite mineral information and data". http://www.mindat.org/min-42463.html. Retrieved 2016-03-04. 
  3. Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine 85 (3): 291–320. doi:10.1180/mgm.2021.43. Bibcode2021MinM...85..291W.