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Automated Microscope‐Absorption‐Spectrophotometry Of Rock‐Forming Minerals In The Range 40,000–5000 Cm −1 (250–2000 Nm)
Author(s) -
Langer K.,
Frentrup K.R.
Publication year - 1979
Publication title -
journal of microscopy
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.569
H-Index - 111
eISSN - 1365-2818
pISSN - 0022-2720
DOI - 10.1111/j.1365-2818.1979.tb00216.x
Subject(s) - absorbance , absorption (acoustics) , analytical chemistry (journal) , spectral line , absorption spectroscopy , ion , silicate , microscope , absorption band , materials science , chemistry , optics , physics , organic chemistry , chromatography , astronomy , composite material
SUMMARY To measure polarized absorption spectra of microcrystals of 3d n ‐ion bearing silicate minerals, computer processed, microscope‐spectrophotometric methods have been developed. Absorbance, log ( I 0 / I ), can be measured with high relative accuracy (near u.v. and vis: ±0·002 to 0·001; n.i.r.: ±0·004 to 0·002), and relatively small spectral band widths are available. Hence, weak spin‐forbidden dd‐bands of 3d n ‐ions can be recognized alongside spin‐allowed dd‐transitions without artificial broadening of absorption bands due to finite resolution. The smallest area from which absorption spectra can be taken is 8 μm in diameter. As one example of the many applications in mineralogy and material sciences, absorption spectra of a natural spessartine garnet, Spess 69·7 Alm 30·0 Gross 0·05 , containing Mn 2+ , Fe 2+ , and traces of Fe 3+ as 3d n ‐ions, and of a pure Mn 2+ ‐garnet, Spess 67 Gross 33 , are presented. From these it is evident that bands in natural spessartines at ∼ 26,900, 23,200 cm −1 which were assigned to dd‐transitions in Fe 3+(6) , have to be reassigned to Mn 2+(8) . Comparison of spectra obtained with the microscopic equipment described with those obtained by means of conventional macroscopic equipment prove that the methods described produce true spectra.