Uses of near-infared spectra for the identification of clay minerals

• A new source of sepiolite was found at the Frisco Chlorite Mine in Inyo Co., CA.
• The NIR overtone bands of phlogopite–biotite, vs. FeO content, are a linear function.
• The correlation of kaolinites and dickites are shown for the NIR combination bands.
• Chlorite mineral NIR first overtone bands, vs. FeO content, give a linear function.
• The differentiation of halloysite and nacrite combination bands is given.

Aspects of clay mineralogy can be determined by the use of near-infrared (NIR) spectra. Beginning with fibrous clay minerals, the combination band spectra do not change position with changes in metal oxide content. Other clay mineral spectra were compared to determine whether this is unusual. These include NIR spectra of chlorite, micas and their alteration products, montmorillonites, and the kaolin group of clay minerals. None are fixed as sepiolite and palygorskite are. For all clay mineral IR spectra only the fibrous clay mineral spectra are fixed. The correlation of the OH fundamental and first overtone OH spectral wave numbers are a constant of 1.955. The kaolin group is readily differentiated by their combination band spectra, such as kaolinite and dickite.