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We present an in-depth study of the reflectance spectra of 39 equilibratedand 41 unequilibrated ordinary chondrites. We demonstrate that consistentmeasuring conditions are vital for the direct comparison of spectral featuresbetween chondrites, otherwise hampering any conclusions. We include acomparison with a total of 466 S-type asteroid reflectance spectra. We analyze(i) if a difference between EOCs and UOCs as well as between H, L and LL can beseen, (ii) if it is possible to identify unequilibrated and equilibrated S-typeasteroid surfaces and (iii) if we can further constrain the match between OCsand S-type asteroids all based on reflectance spectra. We checked theclassification of the 31 Antarctic UOCs analyzed in the present work, usingpetrography and magnetic measurements, and evidenced that 74% of them weremisclassified. Reflectance spectra were compared between EOCs and UOCs as wellas between H, L and LL chondrites using a set of spectral features includingband depths and positions, peak reflectance values, spectral slopes and theOl/(Ol + Px) ratio. UOCs and EOCs reflectance spectra show no clear-cutdichotomy, but a continuum with some EOCs showing stronger absorption bands andpeak reflectance values, while others are comparable to UOCs. We show by theexample of 6 EOCs that their band depths decrease with decreasing grain size.Based on reflectance spectra alone, it is thus highly challenging toobjectively identify an unequilibrated from an equilibrated S-type surface.There is no clear distinction of the chemical groups: only LL EOCs ofpetrographic type > 4 can be distinguished from H and L through less deep 2-micband depths and 1-mic band positions at longer wavelengths. Lastly, ananti-correlation between the diameter of the asteroids and their 1000 nm banddepth is found indicating that larger sized S-type asteroids show finer grainedsurfaces.

Investigating S-type asteroid surfaces through reflectance spectra of Ordinary Chondrites