corundum, sources.12, gems

Descriptions are given of gem-quality sapphire and “hyacinth” zircon—and the associated chrome spinel, magnetite, and enstatite—found at Primorye in heavy-mineral concentrates that were ultimately derived from alkali basalts. Transparent blue, blue-green, green, and occasional multicolored sapphires are found as rounded pebbles (2 to 30 mm in size); some star sapphires are recovered. Chemical analyses and visible absorption spectra show that the sapphire coloration is related to the presence of Fe (0.72–1.75 wt.% FeO) and Ti (0.02–0.20 wt.% TiO₂). Inclusions of hercynite and ferrocolumbite were identified in some of these corundums. The zircon also is found as rounded pebbles (1 to 25 mm in size). They are transparent orange, orange-yellow, or brown-red, and become colorless on heating. Their chemical compositions correspond to those of the rare zircon variety naegite, with 4.59–6.14 wt.% Ta₂O₅, 3.22–3.59 wt.% Nb₂O₅, and 3.98–4.09 wt.% ThO₂. [Editor’s note: The terms hyacinth and naegite are not used in most modern gemology and mineralogy references in English.]