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Typical Minerals
Volcanic Glass. Obsidian has cooled too quickly for minerals to form. Chemical composition, however, will be from the bottom of Bowen's Reaction series (i.e. felsic).
     We typically associate obsidian with very black, shiny, glassy, with conchoidal fracture (smooth curved breaks, often with concentric ridges.) This specimen is the less common red variety.
     The fact that this is glass means it has no minerals because it cooled too quickly for them to form. The glass is opaque because it is "dirty" filled with inclusions and a lot of chemical elements.
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Tectonic Association
      Associated with felsic volcanism on the continents.
   Tectonic Cross Section - pdf version

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