The new mineral gazeevite,
BaCa6(SiO4)2(SO4)2O
(R3m, a = 7.1540(1),
c = 25.1242(5) Å, V = 1113.58(3)
Å3, Z = 3), was found in an altered xenolith
in rhyodacites ofthe Shadil-Khokh volcano, Southern Ossetia and at three
localities in larnite pyrometamorphic rocks of the Hatrurim Complex; Nahal
Darga and Jabel Harmun, Judean Mountains, Palestinian Autonomy, and Har
Parsa, Negev Desert, Israel. Larnite, fluorellestadite–fluorapatite,
srebrodolskite–brownmilleriteand mayenite-supergroup minerals are the main
minerals commonly associated with gazeevite. Gazeevite is isostructural with
zadovite and aradite; the 1:1 type AB6(TO4)2(TO4)2W, occurs together with the structurallyrelated minerals of
the nabimusaite series, 3:1 type AB12(TO4)4(TO4)2W3, where A = Ba, K, Sr...; B =
Ca, Na...; T = Si, P, V5+, S6+,
Al...; W = O2–,F–. Single
antiperovskite layers {[WB6](TO4)2} in the structure type of gazeevite–zadovite and
triple {[W3B12](TO4)4} layers in arctite–nabimusaite areintercalated
with single A(TO4) layers. These minerals with an interrupted antiperovskite
structure are characterized by a modular layered structure derived from
hatrurite, Ca3(SiO4)O. Gazeevite is colourless,
transparent, with a white streakand vitreous lustre. Gazeevite is brittle,
shows pronounced parting and imperfect cleavage on {001}; it is uniaxial
(–), ω = 1.640(3), ε = 1.636(2) (λ = 589 nm) and nonpleochroic; Mohs'
hardness is ∼4.5, VHN50 = 417 kg mm–2. The calculateddensity is =
3.39 g cm–3. The main lines of the calculated powder X-ray
diffraction pattern are as follows
(d(Å)/I/hkl):
3.58/100/110, 3.07/91/021, 2.76/47/116, 1.789/73/220, 3.29/60/113,
2.78/36/024, 2.12/25/125, 2.21/21/208. Raman spectra of gazeeviteare
compared with spectra of other minerals. The formation of gazeevite and
minerals of the nabimusaite–dargaite series is connected with
high-temperature alteration of an early assemblage of clinker minerals
affected by later fluids generated by volcanic activity or combustion
processes.