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The B K-edge spectra of a wide variety of minerals have been measured using the technique of parallel electron energy-loss spectroscopy (PEELS) conducted in a scanning transmission electron microscope (STEM) from sample areas of nanometer dimensions. The B K edges of the minerals exhibit electron energy-loss near-edge structure (ELNES) characteristic of B coordination. For threefold-coordinated B ( [3] B), the spectra are domi­nated by a sharp peak at ca. 194 eV because of transitions to unoccupied states of π* character, followed by a broader peak at ca. 203 eV attributed to states of σ* character. The ELNES on the B K edge (B K ELNES) of fourfold-coordinated B ( [4] B) consists of a sharp rise in intensity with a maximum at ca. 199 eV followed by several weaker structures. For  [4] B, the ELNES is interpreted as transitions to states of antibonding σ* character. Minerals that possess both  [3] B and  [4] B exhibit an edge shape that is composed of B K edges from the respective BO 3  and BO 4  units, and we demonstrate the feasibility of quan­tification of relative site occupancies in minerals containing a mixture of B coordinations. The origins of the B K ELNES are discussed in terms of both molecular orbital (MO) and multiple scattering (MS) theory. We also present the B K-edge spectra of selected non­minerals and show how differences in edge shapes and energy onsets allow these nonmi­nerals to be readily distinguished from borates and borosilicates.

Parallel electron energy-losss pectroscopy( PEELS) study of B in minerals: The electron energy-loss near-edge structure (ELNES) of the B K edge