Sources

The data presented in this database are mid-infrared FTIR spectra mainly published in following papers:
Weber I., Morlok A., Bischoff A., Hiesinger H., Ward D., Joy K.H., Crowther S.A., Jastrzebski N.D., Gilmour J.D., Clay P.L., et al. (2016) Cosmochemical and spectroscopic properties of Northwest Africa 7325—A consortium study. Meteoritics & Planetary Science 51, 3-30.

Morlok A., Stojic A., Dittmar I., Hiesinger H., Tiedeken M., Sohn M., Weber I., Helbert J. (2016) Mid-infrared spectroscopy of impactites from the Nördlinger Ries impact crater. Icarus 264, 352-368.

Morlok A., Stojic A., Weber I., Hiesinger H., Zanetti M., Helbert J. (2016) Mid-infrared bi-directional reflectance spectroscopy of impact melt glasses and tektites. Icarus 278, 162-179.

For details (e.g. composition) about the samples, we refer to these publications. Further data are also available upon request.

Sample Preparation

For all grain size fractions, the bulk sample material was ground in steel and agate mortars and cleaned by using acetone. The material was dry sieved for one hour into four fractions: 0-25 µm, 25-63 µm, 63-125 µm, and 125-250 µm. The larger two fractions were cleaned again with acetone, to remove finer particles. For additional analyses using micro-FTIR, we produced thick or standard polished petrological thin sections.

Sample Characterization

Samples were characterized using Optical Microscopy, Scanning Electron Microscopy (SEM) with EDX (Energy Dispersive X-Ray Spectroscopy), and, in some cases, Electron Probe Micro Analyzer (EPMA) and Raman spectroscopy. (Further details can be found in the publications.)

Diffuse reflectance/Bi-directional reflectance FTIR-Analyses

Each size fraction was gently placed in an aluminum sample cup (1 cm diameter, 1.5-3 mm deep). The surface was flattened with a spatula to create a uniform surface.
Analyses in the mid-infrared (2.5-19 µm) were made using a Bruker Vertex 70 infrared system with a MCT detector at the IRIS (Infrared and Raman for Interplanetary Spectroscopy) laboratory at the Institut für Planetologie (Münster).
Measurements usually were made under low pressure (10-3 bar). In some cases, investigations in ambient air were necessary due to pore collapse problems, which may have resulted in water and atmosphere-related bands in the spectral range below 7 µm.
We accumulated 512 scans for each size fraction at an aperture of 2.5 mm, using a background calibration a diffuse gold standard (INFRAGOLD^TM).
To emulate different observational geometries of an orbiter, we obtained analyses with a variable geometry stage (Bruker A513). The spectra were taken in a specular geometry of 30° incidence (i) and 30° emergence angle (e), and in 20° incidence (i) and 30° emergence angle (e).

Micro-FTIR

We used a Bruker Hyperion 2000 IR microscope attached to the external port of a Bruker Vertex 70v at the Hochschule Emden/Leer for micro analyses. Here a 250×250 µm² to 1000×1000 µm² sized apertures was used to obtain in-situ reflectance spectra on polished thin sections. For each spectrum, 128 scans were added. A gold mirror was used for background calibration.