Isomorphic sodium admixture in garnets formed at high pressures

摘要: Na2O contents were determined by electron microprobe analysis in 124 garnets from diamonds, xenoliths of peridotites, eclogites kimberlitic pipes and metamorphic complexes. content ranges between 0.01 0.22% with the limit detection at about 0.01%. In diamond-bearing orange diamonds a regular increase has been established, varying 0.09 to 0.22, as compared complexes (range 0.06). It is assumed that increased mainly connected higher pressure, whereas isomorphism sodium initial stages transition Si4 Si6 garnet structure: CaAl⇄NaSi.