<
p id="
p-1">Irinarassite, Ca
3Sn
2SiAl
2O
12, a new mineral s
pecies of the garnet su
pergrou
p was discovered in metasomatically altered carbonate-silicate xenoliths in ignimbrites of the U
pper Chegem Caldera, Northern Caucasus, Kabardino-Balkaria, Russia. It occurs as small zones and irregular s
pots in kimzeyite-kerimasite or rarely as single crystals not exceeding 10 μm in size, within com
plex
pseudomor
phs after zircon. Lakargiite, tazheranite, baddeleyite, kerimasite, kimzeyite, baghdadite and rarely magnesioferrite are associated with irinarassite in the
pseudomor
phs which are confined to larnite-cus
pidine zones immediately adjoining the ignimbrite. Larnite, cus
pidine, rondorfite, fluor- and hydroxylellestadite, fluorite and secondary minerals such as ettringite, hillebrandite and bultfonteinite are associated with irinarassite. Irinarassite is
pale brown to yellow colour. The mineral is characterized by the absence of cleavage and by an irregular fracture. The calculated density is 4.3 g cm
p>−1p>. The mineral is isotro
pic with a calculated refractive index of 1.9. The em
pirical crystal chemical formula of irinarassite from the holoty
pe s
pecimen is as follows (Ca
2.965pan class="inline-formula" id="inline-formula-1"> pan>)
Σ3(Sn
1.016Zr
0.410Ti
0.262pan class="inline-formula" id="inline-formula-2"> pan>
pan class="inline-formula" id="inline-formula-3"> pan>
pan class="inline-formula" id="inline-formula-4"> pan>Sc
0.014Hf
0.006Nb
0.004)
Σ2.001(Al
1.386pan class="inline-formula" id="inline-formula-5"> pan>Si
0.446pan class="inline-formula" id="inline-formula-6"> pan>)
Σ3O
12. Electron backscatter diffraction
patterns of irinarassite are fitted to the garnet model with
a = 12.50(3) Å with excellent MAD (mean angular deviation) = 0.16°. The Raman s
pectrum of irinarassite is analogous to those of kerimasite and other Zr-Sn-garnets of the schorlomite and bitikleite grou
ps.
p>