The variation of tetrahedral bond lengths in sodic plagioclase feldspars
Abstract
Multiple linear regression analysis has been applied to the geometric and chemical variables in sodic plagioclases in order to determine their relative effects on individual TO bond lengths in the Al_{1+x}Si_{3x}O_{8} tetrahedral framework. Using data from crystal structure analyses of low and high albite, An_{16} and An_{28}, and assuming that low albite is completely ordered, 1 410_2004_Article_BF00376472_TeX2GIFE1.gif begin{gathered} {text{T}}  {text{O = 1}}{text{.568}} + {text{[(0}}{text{.122) x (Al content of the T site)]}} \ {text{ }}  {text{[(0}}{text{.037) x (}}Δ {text{Al}}_{{text{br}}} )] + [0.063){text{ x }}(Σ {text{[}}q{text{/(Na,Ca}}  {text{O)}}^{text{2}} ])] \ {text{ }} + {text{[(0}}{text{.029) x (}}  {text{1/cosT}}  {text{O}}  {text{T)]}} \ where the Al content of a particular tetrahedral (T) site can be estimated from empiricallyderived determinative curves, where Δ Al_{br} is a linkage factor to account for the Al content of adjacent tetrahedral sites, where the formal charge on the (Na_{1x}Ca_{x}) atom is q=1+x, and where TOT is the intertetrahedral angle involving the TO bond. For sodic plagioclases it is essential to know only the anorthite content and the 2Θ_{131}2Θ_{1¯31} spacing (Cu K _{α} radiation) in order to determine the independent variables in this equation and thus to evaluate the individual TO distances. The 64 individual TO distances predicted for the four sodic plagioclases by this equation agree well with the observed TO bond lengths (σ=0.004 Å; r=0.994), and the method has been used by way of example to rationalize the TO bond lengths in analcime (cf. Ferraris, Jones and Yerkess, 1972).
 Publication:

Contributions to Mineralogy and Petrology
 Pub Date:
 December 1973
 DOI:
 10.1007/BF00376472
 Bibcode:
 1973CoMP...39..327P