Electrostatic characterization of oxygen sites in minerals
Electrostatic characterization of oxygen sites in minerals
复制标题
矿物中氧位点的静电表征
DOI：
10.1016/0016-7037(89)90215-9
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发表时间：
1989
影响因子：
5
通讯作者：
J. Smyth
中科院分区：
文献类型：
--
作者：
J. Smyth
计算了165个成岩矿物端元中约500个阴离子中心的静电势，并给出了配位数、配位阳离子和平均阳离子-阴离子距离。计算得到的各氧位的静电势范围为：(β-Mg_2SiO_4(瓦斯利石))O_2位的最低值19.56V，到钠硝化钠的最高值36.4V，未加权平均值为28.58V，标准差为2.51V。位电位与配位数成反比，因此在硅酸盐中，桥氧位的电势最高，与硅键合的氧的电势较低，而未与硅键合的氧的电势最低。羟基氧(具有确定的H位)的位置电位平均为28.3V，标准偏差为2.0V。不含H的氟位和羟基位置的电位作为−1的单电荷模拟的范围为10.3V至16.8V，其平均值为10.87，标准偏差为1.85V，可与配位阳离子类型一起用于确定矿物中可能的羟基取代位。各种矿物的平均氧位位势按单位晶胞中的位点数加权，范围从低的石灰(CaO)20.9V到高的36.4V(纯碱)，并与观察到的矿物中氧同位素分馏趋势密切相关。这种相关性对含有轻阳离子的矿物最好(Z<；20)，因此氧位位势较大的矿物倾向于浓缩较重的氧同位素。这种相关性足够好，可以定性地估计未经实验测量的高压硅酸盐等矿物的氧同位素分馏系数。随着矿物对之间氧同位素分馏实验测量的进一步开展，基于阴离子位置的静电位电势定量预测同位素分馏因子成为可能。
The electrostatic potentials of approximately 500 anion sites in 165 rock-forming mineral end-members have been computed and presented along with coordination numbers, coordinating cations, and mean cation-anion distances. The electrostatic potentials computed for the individual oxygen sites range from a low of 19.56 v for the O2 site of (β-Mg2SiO4(wadsleyite) to a high of 36.4 v for soda niter, with an unweighted average of 28.58 v and standard deviation of 2.51 v. The site potentials tend to vary inversely with coordination number, so that in the silicates the bridging oxygen sites have the highest potentials, oxygens bonded to one Si have lower potentials, and oxygens not bonded to silicon have the lowest. The site potentials of hydroxyl oxygens (with well-determined H-positions) average 28.3 v with a standard deviation of 2.0 v. The potentials of fluorine sites and hydroxyl sites modeled without the H, as a single charge of −1, range from 10.3 v to 16.8 v, with an average value of 10.87 and a standard deviation of 1.85 v. The electrostatic site potentials may thus be used along with coordinating cation types to identify possible sites for hydroxyl substitution in minerals.The average oxygen site potentials for various minerals weighted on the number of sites per unit cell range from a low of 20.9 v for lime (CaO) to a high of 36.4 v for soda niter and are strongly correlated with observed oxygen isotope fractionation trends in minerals. This correlation is best for minerals containing light cations (Z< 20), so that minerals with larger oxygen site potentials tend to concentrate the heavier oxygen isotope. This correlation is sufficiently good to permit qualitative estimation of oxygen isotope fractionation factors of minerals such as high-pressure silicates that have not been measured experimentally. With further work on experimental measurement of oxygen isotope fractionation between mineral pairs, quantitative prediction of isotope fractionation factors may become possible based on electrostatic site potentials of anion sites.