Si-Al ordering in nephelines

Different degrees of Si-Al ordering are demonstrated to exist in nepheline on the basis of five crystal structure refinements on specimens with different geologic origins and laboratory treatments. Disorder increases in the sequence; gneissic-igneous plutonic-volcanic nepheline and appears to increase as a result of laboratory heat treatment. The four independent tetrahedral sites can be divided into two pairs with one pair of sites always less ordered than a second pair in a simple regular relationship.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/47315/1/410_2004_Article_BF00372253.pd