| Ferrokentbrooksite | |
|---|---|
Ferrokentbrooksite, Amphibole Supergroup-166795
| |
| General | |
| Category | Cyclosilicate |
| Formula (repeating unit) | Na15Ca6(Fe,Mn)3Zr3NbSi25O73(O,OH,H2O)3(Cl,F,OH)2 (original form) |
| IMA symbol | Fktb[1] |
| Strunz classification | 9.CO.10 (10 ed) 8/E.23-15 (8 ed) |
| Dana classification | 64.1.2.2 |
| Crystal system | Trigonal |
| Crystal class | Ditrigonal pyramidal (3m) H-M symbol: (3m) |
| Space group | R3m |
| Unit cell | a = 14.25, c = 30.03 [Å] (approximated); Z = 3 |
| Identification | |
| Color | Reddish brown to red |
| Crystal habit | Pseudo-octahedra |
| Cleavage | No |
| Fracture | Uneven to conchoidal |
| Luster | Vitreous |
| Streak | White |
| Diaphaneity | Transparent |
| Refractive index | nω = 1.62, nε = 1.62 (approximated) |
| Common impurities | REE (mainly Ce and Y), K, Sr |
| References | [2][3] |
Ferrokentbrooksite is a moderately rare mineral of the eudialyte group,[2] with formula Na15Ca6(Fe,Mn)3Zr3NbSi25O73(O,OH,H2O)3(Cl,F,OH)2.[3] The original formula was extended form to show the presence of cyclic silicate groups and presence of silicon at the M4 site, according to the nomenclature of eudialyte group.[4] As suggested by its name, it is the (ferrous) iron analogue of kentbrooksite.[3] When compared to the latter, it is also chlorine-dominant instead of being fluorine-dominant.[2] The original (holotype) material is also relatively enriched in rare earth elements, including cerium and yttrium.[3]
Ferrokentbrooksite was discovered in Mont Saint-Hilaire, Quebec, Canada – a site wealth in rare alkaline minerals.[5] At the site ferrokentbrooksite coexists with aegirine, albite, ancylite-(Ce), calcite, catapleiite, fluorite, fluorapatite, gonnardite, microcline, natrolite, nepheline, rhodochrosite, and serandite.[3]
Beside fluorine, ferrokentbrooksite has admixtures of rare earth elements (including cerium, yttrium, lanthanum, neodymium and some gadolinium and samarium), potassium, strontium, and contains minor admixtures of titanium, hafnium, and tantalum.[3]
Iron in ferrokentbrooksite has coordination number 5.[3]
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