2元素的地球化学亲和性(68).ppt

第二章 自然体系中元素共生结合规律 一、元素的地球化学亲和性 二、类质同像代换及微量元素共生结合 规律 三、晶体场理论在解释过渡族元素结合 规律上的应用 To first order, the distribution of elements between core and mantle resembles equilibrium partitioning between metal liquid and silicates…confirmed by iron and achondrite meteorites (but at high P, no separate sulfide phase) achondrite [eik?ndrait] n. 不含球粒陨石 Behavior of elements: Goldschmidt’s classification Elements divided into four broad categories: Lithophile generally found within crust and mantle Concentrate in silica-rich melts 元素结合规律可从两个角度来衡量 1.从能量的角度 电负性（X） (Electronegativity): 原子在其外层吸引其他电子的能力 电离势（I） 电子亲和能（E）、 Pairs of atoms with nearly equal electronegativity share electrons in covalent bonds(共价键). This is the dominant bonding process in organic compounds, sulfides, and compound anions (CO32-, SO42-, etc.). Elements with intermediate electronegativity and full or empty d-shells are happiest in covalent bonds with S and are therefore chalcophile. Elements with intermediate electronegativity and ~4 to ~8 d electrons are stabilized in neutral metallic bonding environments and tend to be siderophile. 2.从空间几何形式的角度 半径（原子、离子）、 配位数、 原子和离子极化、 最紧密堆积等。 Ionic (and Ionic-Covalent) Structures R-cation/R-anion Coordination (# anions( 阴离子)/cation（阳离子） 1 12 (CCP, HCP) O.732-1.0 8 (BCC) 0.414-0.732 6 (Rutile) 0.225-0.414 4 (SiO2) 0.155-0.225 3 (Calcite) 0.155 2 Ions whose radii differ by less than 15% readily substitute each other Ions whose charge differ by one unit can substitute if coupled to a suitable charge-balancing substitution; ions differing by more than one charge do not substitute extensively. In any substitution the ion with the higher ionic potential (charge/radius) forms a stronger bond and a more stable mineral Ions with very different electronegativity will not substitute much even if charge and radius match 不同成因的磁铁矿具有不同的标型元素组合： 基性，超基性：富Cr3+、 V3+、 Ti4+、 Mg 2+、 Ni 2+、 Co 2+，贫Al 3+； 酸性，碱性岩：