8) Pumice and obsidian are both forms of volcanic glass. What are one similarity and one difference in the
composition of these two rocks? (p.150)
pumice
• igneous extrusive rock
composed largely of silica;
light in color, light enough to
float on water
• commonly used in soaps
and cleansers, concrete and
plaster
obsidian
igneous extrusive rock
composed largely of silica:
dark due todark-colored
minerals distributed within
• commonly used to make
jewelry and surgical
instruments

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