Faizievite

Faizievite is a very rare mineral^[3] with the formula K₂Na(Ca₆Na)Ti₄Li₆Si₂₄O₆₆F₂.^[2] This triclinic mineral is chemically related to baratovite and katayamalite.^[4][5] Faizievite is a single-locality mineral, coming from the moraine of the Darai-Pioz glacier, Tien Shan Mountains, Tajikistan. Alkaline rocks of this site are famous for containing numerous rare minerals, often enriched in boron, caesium, lithium, titanium, rare earth elements, barium, and others.^[6]

Faizievite
General
Category	Silicate mineral, Cyclosilicate
Formula	K2Na(Ca6Na)Ti4Li6Si24O66F2
IMA symbol	Fai[1]
Dana classification	63.2.10.1
Crystal system	Triclinic
Crystal class	Pinacoidal (1) (same H-M symbol)
Space group	P1
Unit cell	a = 9.82, b = 9.82 c = 17.31 [Å], α = 99.209(2)° β = 94.67(2)°, γ = 119.839(1)° (approximated); Z = 1
Identification
Color	Colorless
Crystal habit	tabular plates
Cleavage	None
Tenacity	Brittle
Mohs scale hardness	4-4.5
Luster	Vitreous
Diaphaneity	Opaque
Density	2.83 (measured)
Optical properties	Biaxal (+)
Refractive index	np=1.65, nm=1.66 (approximated)
2V angle	-72o (measured), -70o (calculated, approximated)
References	[2][3]

Occurrence and association

Faizievite was detected in quartz boulders, together with aegirine, baratovite, fluorite, leucosphenite, pectolite, and polylithionite.^[2]

Notes on chemistry and structure

Strontium and trace amounts of rubidium, barium and niobium are present in the structure of faizievite. One of the sodium sites is partially vacant, and fluorine may be substituted by oxygen.^[2]

Relation to other minerals

Faizievite is related to beryl and osumilite groups of minerals.^[3]