Elemental analysis of Australian amorphous banded opals by laser-ablation ICP-MS
Brown, Leslie D.; Ray, Abhi S.; Thomas, Paul S.
published: Aug 20, 2004
Several banded Australian opal-AG samples were analysed by laser ablation ICP-MS. The banded opals studied contained darker-coloured black or grey bands adjacent to lighter-coloured white or clear bands. The elemental distribution between bands indicated that darker-coloured bands contained significantly higher concentrations of transition elements (Ti, Co, V, Ni, Cu, Zn and Y) and rare-earth elements (La, Ce) than lighter-coloured bands. A solution depletion model, involving the charge-neutralisation of silica colloids by highly-charged transition metal cations, is proposed to explain these results. Irrespective of the origin of the opal, the distribution of trace elements for the white, translucent and play of colour opal bands was observed to be similar. This similarity was consistent with the proposed model.