Obsidian – volcanic glass Glassy texture indicates quenched lava Size: 10 cm Green Obsidian – Volcanic glass Glassy texture indicates instant cooling Size: 10 cm Obsidian with Feldspars Microlites Two phases of cooling: one slow, one instant Size: 10 cm Pitchstone – Volcanic Glass with dull pitchlike luster Contains microcrystalline embryonic crystals indicating rapid cooling Size: 10 cm Rhyolite - Fine-grained volcanic rock Fine-grained crystalline texture indicates fast cooling Size: 11 cm Porphyritic Rhyolite with Euhedral Feldspars Two phases of cooling: one slow, one fast Size: 12 cm Equigranular Granite – coarse-grained plutonic rock Coarse-grained crystalline texture indicates slow cooling Size: 12 cm Pegmatite – plutonic rock with high water content Large mineral grain sizes indicates very slow cooling Size: 20 cm