EPS 214: Physical Volcanology
In this lab we will continue to study and interpret structures
in obsidian. In particular, we will focus on the interactions between
various scales of microstructure. The sample we will study is
from Deadman Dome, CA (picture below). This is the obsidian flow
south of Obsidian Dome (see previous lab).
South Deadman flow, CA; photo by R.A. Bailey
There is only one thin section and one hand sample for this
- What is the large (>1 cm diameter) phenocryst?
- Notice that there are many scales (sizes) of crystals. Examine
theses crystals and then define and subdivide them into
distinct ``populations'', if possible. What criteria did you
- What are the compositions and properties of the crystals
in each population?
- Where and under what conditions did each population of
Notice how the ``flow'' bands are deformed around the large
phenocryst. Can you determine the type of deformation
this sample experienced?
Last modified 10 February 2002
Return to Michael's