MEGAKALSILITE, A NEW POLYMORPH OF KAlSiO4 FROM THE KHIBINA ALKALINE MASSIF, KOLA PENINSULA, RUSSIA: MINERAL DESCRIPTION AND CRYSTAL STRUCTURE

Abstract

Megakalsilite, KAlSiO 4 , hexagonal, a 18.1111(8), c 8.4619(4) Å, V 2403.7(2) Å 3 , c:a = 0.4672, space group P6 3 , Z = 24, R = 0.039 (for 3255 observed reflections collected with a four-circle X-ray diffractometer), is a new mineral species from Mount Koashva, Khibina alkaline massif, Kola Peninsula, Russia. It is of pegmatitic origin. Associated minerals are K-feldspar, sodalite, cancrinite, natrolite, pectolite, aegirine, natrite, nacaphite, vitusite, fluorcaphite, belovite, umbite, lemmleinite-K, lomonosovite, lovozerite, phlogopite, sphalerite, and galena. The mineral was found in only one hand specimen of pegmatite rock as a corroded, irregularly shaped grain 2 ϫ 3 mm across, intergrown with cancrinite, sodalite, and natrite. It is transparent, colorless with a white streak, a vitreous luster, and fluoresces pale whitish green under ultraviolet light. Megakalsilite has a Mohs hardness of 6, is brittle with a conchoidal fracture, and has no cleavage. D meas is 2.58 (2)

The Stuffed Framework Structure of SrP2N4: Challenges to Synthesis and Crystal Structure Determination

“…Description of the structure: The framework structure of SrP 2 N 4 is isotypic with the TX 2 -framework structures (T = tetrahedral coordinated atom, Ga, Al, Si, Ge, Zn, P, Co; X = O) of BaGa 2 O 4 , [17] KAlGeO 4 , [19] KCoPO 4 , [46] and KZnPO 4 , [47] which correspond with the megakalsilite (KAlSiO 4 ) structure type [48] being a stuffed framework structure consisting of sequences of tetrahedral layers. Each layer perpendicular to [001] is built up from rings made of six corner-sharing PN 4 tetrahedrons (6-rings).…”

Synthesis and Crystal Structure of the New High‐Pressure Phase CdB2O4

“…Related compounds: The structure of CdB 2 O 4 is closely related to the structure-type of the compounds BaGa 2 O 4 , [32] KAlSiO 4 , [33] KGeAlO 4 , [34,35] KCoPO 4 , [36] CaP 2 N 4 , [37] and SrP 2 N 4 . [38] Both structure types consist of layers of tetrahedra, forming "sechser" rings [39,40] with an identical orientation of the tetrahedra.…”

“…Table 2 In SrP 2 N 4 , this superstructure is caused by avoiding one P À N À P angle of 1808 at nitrogen N15. The isotypic compounds BaGa 2 O 4 , [32] KAlSiO 4 , [33] KGeAlO 4 , [34,35] KCoPO 4 , [36] and CaP 2 N 4 [37] do not show the linear arrangement at the corresponding position. By contrast, the associated BÀOÀB angle in CdB 2 O 4 adopts a value of 1808 at oxygen O1 on thermal average ( Figure 6).…”

“…We report the synthesis and the crystal structure of this compound, including a comparative discussion concerning the related structures of BaGa 2 O 4 , [32] KAlSiO 4 , [33] KGeAlO 4 , [34,35] KCoPO 4 , [36] CaP 2 N 4 [37] and SrP 2 N 4 . [38] In contrast to CdB 2 O 4 , all these phases form a superstructure, whereas CdB 2 O 4 exhibits the basic structure of this family for the first time.…”

Monoclinic structure and nonstoichiometry of `KAlSiO4-O1'

“…Adjacent sheets of tetrahedra are connected by bridging apical O atoms. It should be noted that megakalsilite (KAlSiO 4 ; Khomyakov et al, 2002) is a topological variant of tridymite, with UDUDUD and UUUDDD rings in the ratio 1:3. In contrast with tridymite, which contains only six-membered rings, the framework topology of KAlSiO 4 -O1 includes four-, six-, eight-and ten-membered rings of tetrahedra.…”