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In the visible and near-visible infrared (VNIR) region (0.4-2.5 ym), limonite minerals have strong absorptions below 0.55-0.6 ym and at 0.9 ym, and clays, dioctahedral micas, pyrophyllite, and alunite have a sharp absorption band between 2.15 and 2.25 ym.
Ashley et al. (Tue,) studied this question.
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