What Makes A Mineral A Gemstone?
As mentioned, gems appear coloured due to some of the white light being absorbed within the minerals structure. Most gems are coloured by a limited number of metals present either as impurities, as in Allochromatic gems or as essential constituents of the atomic structure, as in Idiochromatic gems. The most common minerals affecting colour are; Chromium, Iron, Manganese, Titanium and Copper. It is Chromium which produces the intense red of Ruby and the brilliant green of Emerald. In Garnet, Spinel, Sapphire, Peridot and Chrysoberyl it is Iron that is responsible for the more subtle red, blue and yellow colours. The best Sapphires are coloured by both Titanium and Iron whilst copper is responsible for the blue and green of Turquoise and Malachite, and Manganes the pink of Rhodonite. RUBY FACET Some minerals give us more than one gem type. This is because the impurity, which is only a minute amount, is not always the same and may even be a combination of impurities. The interaction of th
