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