Crystals of montgomeryite were placed on a polished metal
surface on the stage of an Olympus BHSM microscope, which is
equipped with 10×, 20×, and 50×
objectives. The microscope is part
of a Renishaw 1000 Raman microscope system, which also includes
a monochromator, a filter system and a CCD detector (1024 pixels).
The Raman spectra were excited by a Spectra-Physics model 127
He–Ne laser producing highly polarised light at 633 nm and collected
at a nominal resolution of 2 cm−1 and a precision of
±1 cm−1
in the range between 100 and 4000 cm−1. Repeated acquisition on
the crystals using the highest magnification (50×) was accumulated
to improve the signal to noise ratio in the spectra. Spectra
were calibrated using the 520.5 cm−1 line of a silicon wafer.