Characterization of obsidian from North Macedonia.

Obsidian is a naturally occurring volcanic glass formed as an extrusive igneous rock. It is produced during the process of rapidly cooling of the extruded felsic lava from a volcano manifesting thereby minimal crystal growth. The subject obsidian was found as impurity in the perlite from the Mariovo region. It is found in tiny black crystals with irregular shapes. The XRPD analysis shows predominantly amorphous glassy phase with minor peaks of the following minerals: anorthite, muscovite, quartz, cristobalite and feldspars. SEM examinations confirmed the glassy structure with presence of certain phases that are most likely due to the clay impurities. [ABSTRACT FROM AUTHOR]