Falsterite
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]
| 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] |
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
- 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
- "Falsterite: Falsterite mineral information and data". Mindat.org. Retrieved 2016-03-04.
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