Cation ordering in synthetic and natural Ni-Mg olivine

Journal Article · Thu Jan 01 00:00:00 EST 1981 · Am. Mineral.; (United States)

OSTI ID:5203665

Bish, D L

The crystal structures of natural liebenbergite-(Ni/sub 1.52/Co/sub 0.05/Fe/sub 0.09/Mg/sub 0.34/)SiO/sub 4/-from Barberton, South Africa, and of synthetic liebenbergite-(Ni/sub 1.16/Mg/sub 0.84/)SiO/sub 4/-synthesized at 500/sup 0/C, have been studied in order to determine the intracrystalline Ni-Mg distribution. The natural liebenbergite is fully ordered, with Ml occupied only by Ni, whereas the synthetic sample is only partially ordered with K/sub D/ = (Mg(M2) . Ni(Ml))/(Ni(M2) . Mg(Ml)) = 9.9(4), ..delta..G/sup o//sub ex/ = -3.5 kcal/mole. Comparison with the results of Rajamani et al. (1975), who found K/sub D/ = 9.2(2) and ..delta..G/sup o//sub ex/ = -6.9 kcal/mole for a sample synthesized at 1280/sup 0/C, implies that the 500/sup 0/C synthetic sample in the present study crystallized metastably in a disordered or partially ordered state and ordering proceeded slowly. Although site size effects are small in Fe-Mg, Ni-Mg, and Co-Mg olivines, the crystal field stabilization energy is important in determining the observed cation distribution in Ni-Mg and Co-Mg olivines. Electronegativity or covalency effects are known only qualitatively, but there is a preference of less electronegative ions (Mg, Ca) for M2. Ordering of Ni into the Ml site of olivine should appreciably affect Ni partitioning between olivine and melt, and activity-composition relations have been examined assuming ideal solution behavior. Deviations from Raoult's law increase with increasng order, but variations in activity coefficients are less than 10 percent below 10 mole% Ni.

• Research Organization: Harvard Univ., Cambridge, MA
• OSTI ID: 5203665
• Journal Information: Am. Mineral.; (United States), Vol. 66
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
CATIONS
ORDER PARAMETERS
OLIVINE
INTERATOMIC DISTANCES
CRYSTAL STRUCTURE
ELECTRONEGATIVITY
MAGNESIUM
NICKEL
ALKALINE EARTH METAL COMPOUNDS
ALKALINE EARTH METALS
CHARGED PARTICLES
DISTANCE
ELEMENTS
IONS
IRON COMPOUNDS
IRON SILICATES
MAGNESIUM COMPOUNDS
MAGNESIUM SILICATES
METALS
MINERALS
OXYGEN COMPOUNDS
SILICATE MINERALS
SILICATES
SILICON COMPOUNDS
TRANSITION ELEMENT COMPOUNDS
TRANSITION ELEMENTS
580300* - Mineralogy
Petrology
& Rock Mechanics- (-1989)