Strong site preference of Co2+ in olivine, Co1.10Mg0.90SiO4

Crystallographic studies of olivine-related sarcopside-type solid solutions

“…An example will be given. Ghose and Wan (1974) obtained KD(Co,Mg) = 4.2 for an olivine hydrothermally prepared at 1420 K. Disregarding the differences in temperature and pressure, KD(Ni,Co) may be estimated from A^(Ni,Co) « £D(Ni,Mg)/KD(Co,Mg) = 9.9/4.2 » 2 (Me = Co, ME = Mg). Ghose and Weidner (1974) have reported A"D(Mn,Mg) = 0.196 for a synthetic Mg-containing tephroite heat-treated at 1270 K. Accordingly, ^D(Ni,Mn) may be estimated as 9.9/0.196 « 50, so Μη 2 + would be strongly ordered at M 2 in a (hypothetical) Ni,Mn-olivine.…”

Vibrational Spectroscopic Study of the System α-Co2SiO4–α-Ni2SiO4

“…Based on the consideration of larger cation size and smaller CFSE in Co> (6), one may expect that Co> has a tendency to be stronger than that of Ni> for entering the M2 sites. The electrostatic calculations and charge density studies on olivines have suggested that the M2 sites are more ionic than the M1 sites (6), and therefore the more covalent transition metal ions (e.g., Co> and Ni>) should prefer to reside in the M1 sites of the forsterite-based solid solutions (5,6,25,26). The electron a$nity of nickel is stronger than that of cobalt, suggesting that Co> may enrich in the more ionic M2 site of the (Co, Ni) SiO solid solutions.…”

Intermediate States on the Way to Edge‐Sharing BO4 Tetrahedra in M6B22O39⋅H2O (M=Fe, Co)

“…Furthermore, hydrogen bonding can be assumed between the H atoms and the adjacent O atoms (see Figure 5). Under ambient pressure, three-fold-coordinated oxygen atoms can be found in a few minerals like aristarainite [28] strontioginorite ((Sr,Ca) 2 B 14 O 20 (OH) 6 ·5 H 2 O) [29] and tunellite (SrB 6 O 9 (OH) 2 ·3 H 2 O). [27] From the 26 crystallographically independent oxygen atoms, O19, O20, O21 and O22 are bridging three BO 4 tetrahedra simultaneously, whereas all other oxygen atoms link two BO 4 tetrahedra.…”