Multispectroscopic methodology to study Libyan desert glass and its formation conditions

Area of Science:

• Geochemistry
• Mineralogy
• Impact Cratering Studies

Background:

• Libyan desert glass (LDG) is a mysterious melt product with an debated origin.
• Previous studies have focused on LDG surfaces, leaving its internal composition largely unexplored.

Purpose of the Study:

• To investigate the internal structure and composition of LDG specimens.
• To compare internal findings with surface analyses.
• To provide new insights into the origin of Libyan desert glass.

Main Methods:

• Integrated analytical techniques including Raman spectroscopy (point-by-point and imaging).
• Scanning electron microscopy with X-ray microanalysis (SEM-EDS).
• Energy-dispersive micro X-ray fluorescence spectrometry (μ-EDXRF).
• Electron probe micro analyzer (EPMA).
• Optical cathodoluminescence (Optical-CL).

Main Results:

• Discernment of melt flow structures and amorphous matrix.
• Identification of high-pressure minerals (coesite, α-cristobalite) and other phases (gypsum, anhydrite, corundum, rutile, calcite, aragonite).
• Evidence of shock pressures (6-30+ GPa) and temperatures (300-1470 °C) during formation.
• Presence of nitrogen and oxygen gases within bubbles, suggesting terrestrial atmosphere origin during impact.
• High-pressure minerals predominantly found in the inner part of LDG specimens.

Conclusions:

• LDG formation involved significant shock pressures and temperatures consistent with an impact event.
• Internal analysis reveals crucial details about the impact conditions and cooling processes.
• Trapped atmospheric gases support a terrestrial impact origin for LDG.