Falsterite

Falsterite
General
Category Phosphate mineral
Formula
(repeating unit)		 Ca2MgMn2+2(Fe2+0.5Fe3+0.5)4
Zn4(PO4)8(OH)4(H2O)14
Crystal system Monoclinic
Crystal class Prismatic (2/m)
(same H-M symbol)
Space group P21/c
Unit cell a = 6.39, b = 21.26
c = 15.37 [Å]; β = 90.56° (approximated); Z = 2
Identification
Color Greenish-blue
Crystal habit thin plates, rectangular laths
Cleavage {010}, perfect
Fracture Uneven
Luster Vitreous
Streak Very pale greenish-blue
Diaphaneity Transparent
Density 2.78 (measured); 2.84 (calculated; approximated)
Optical properties Biaxal (-)
Refractive index nα=1.58, nβ=1.60, nγ=1.61 (approximated)
Pleochroism Colorless to very pale yellow (X & Z), blue-green (Y)
Dispersion Strong
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 2 3 4 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. 1 2 3 "Falsterite: Falsterite mineral information and data". Mindat.org. Retrieved 2016-03-04.


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