Two blue tourmalines.
Both of these tourmalines are blue because they transmit light in the
500 nm region. The elbaite from Salinas, Minas Gerais, Brazil, owes
its color to Fe2+ whereas the elbaite from Sao Jose de Batalha,
Paraíba, Brazil, owes its color to Cu2+. Although
there are strinking differences in the optical absorption spectra of these
minerals, because they occur predominantly in the near-infrared region
of the spectrum, they have little effect upon the color of the minerals.
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