Micro-spectroscopic characterization of organic and hydrous components in weathered Antarctic micrometeorites

Eight unmelted Antarctic micrometeorite (AMMs) recovered from Kuwagata Nunatak were studied on Al-foils by infrared (IR), Raman, and visible reflection micro-spectroscopy in combination with electron microscopy. Major element abundances of the AMMs studied were found to be similar to solar abundance, although all have the common characteristic of Mg-depletion. Absorption bands around 500 nm were detected for some of the AMMs by the visible micro-spectroscopic method, and these AMMs can be assigned to Fe-hydroxide-like materials. These results suggest that the studied AMMs experienced weathering in Antarctica. Four grains showed the presence of IR H₂O and CH bands similar to those of type 2 carbonaceous chondrites, while these were found to be absent in two grains, as in type 3 carbonaceous chondrites. D (disordered: 1360 cm-1) and G (graphite: 1600 cm^-1) Raman band features of graphitic carbonaceous materials in these AMMs were not similar to those for type 3 but were rather close to those for type 2 and 1 carbonaceous chondrites, although some data showed a degree of deviation. The genetic classification of individual AMM grains can thus be studied by these methods, although the weathering effects and the atmospheric entry heating on organics and hydrous components need to be evaluated. These multiple micro-spectroscopic reflectance methods are useful for the characterization of precious small samples.