Tassieite
Tassieite is an IMA-recognized mineral species in the phosphate class, with the chemical formula NaCa₂Mg₃Fe²⁺₂Fe³⁺(PO₄)₆·2H₂O.
It crystallizes in the orthorhombic crystal system (space group Pbca). It is a member of the Wicksite structural group.
Key properties: specific gravity 3.45; Light green streak; Vitreous luster; optically biaxial.
IMA symbol Tas, IMA status: approved, named in 2005.
A late-stage, low-temperature mineral formed by hydrothermal alteration of stornesite-(Y), wagnerite and fluorapatite in the core of a fluorapatite nodule in regionally metamorphosed and fractured gneissic rocks.
It is found associated with Stornesite-(Y), wagnerite, fluorapatite, xenotime-(Y), mélonjosephite, monazite-(Ce).
The name refers to a lake, Tassie Tarn, near the site from which the first specimens were collected.