Crystal structure of magnesioneptunite

Abstract

The crystal structure of the new mineral magnesioneptunite (K 0.8 Na 0.1 ᮀ 0.1 )Na 2 Li(Ti 0.39 Mg 0.34 Fe 0.27 ) 2 (Ti 0.59 Mg 0.22 Fe 0.19 ) 2 [Si 4 O 11 ] 2 (O,OH) from the xenolith of Verkhneche gemskaya caldera (Lakarga Mountain, North Caucasus) has been investigated by X ray diffraction (XCali bur S diffractometer, R = 0.0244): a = 16.3271 (7) Å, b = 12.4788(4) Å, c = 9.9666(4) Å, β = 115.651(5), V = 1830.5(1) Å 3 , sp. gr. C2/c, Z = 4, and ρ calcd = 3.152 g/cm 3 . The disordered distribution of Ti, Mg, and Fe atoms in the octahedra forming the basis of the cationic framework is established. It is shown that the isomor phic occupation of octahedral positions by cations of three types corresponds to the centrosymmetric crystal structure and is likely caused by the high temperature crystallization of the mineral.

Spectroscopy of selected copper group minerals: ktenasite, orthoserpierite and kipushite

“…The structure consists of sheets containing octahedra and tetrahedra in [(Cu,Zn) 5 [14]. Crystal structure and crystal chemical characteristics of individual Zn phosphate minerals and synthetic compounds have been summarised, and detailed structural data presented by Karimova et al [15] provide the classification of phosphates into three groups: (1) those having acid orthophosphate/diorthophosphate groups and Zn atoms in polyhedra that have a cation function; (2) those in which anion Zn PO 4 3-radicals have a mixed crystal chemical nature and form ZnO 4 -and PO 4 3-tetrahedrons: and (3) those containing both cation constructions of Zn polyhedrons and anion radicals of mixed type [15]. Recently, Raman spectroscopy has been applied to investigate the implications of hydrogen bonding in basic Cu-sulphates including antlerite, brochiantite, posnjakite, langite, wroewolfeite, and selected complex Cu sulphate minerals [16].…”