Cadmium in Minerals from the Skaergaard Intrusion - A Further Study

Cd has been determined in a suite of rocks and minerals from the Skaergaard intrusion, east Greenland by f1ameless atomic absorption spectrophotometry with the heated graphite atomizer. Cd is progressively enriched in the ultimate residual magmatic fractions. Among the minerals studied, Cd shows a distinct preference for ironrich pyroxene, olivine and titaniferous magnetite.

A study of the mode of entry of Cd into the minerals as discussed in terms of the number of Cd²⁺ ions per appropriate structural site reveals that despite the similarity of the ionic radius of Cd²⁺ and Ca²⁺ in octahedral co-ordination, Cd²⁺ ions appear to substitute more for Fe²⁺ in octahedral positions. It has been found that Cd enters octahedral sites in olivine, pyroxene and magnetite in approximately equal amounts. The poor entry of Cd²⁺ ions into the Fe²⁺ site of ilmenite is attributed to its highly distorted octahedral nature in addition to the presence of Fe²⁺ ions in the lattice.