Aa Lava

Aa (ah-ah) lava is cooler and slower-moving; it breaks into jagged chunks.

Andesite Lava

The black crystals in this specimen are the water-bearing minerals amphibole and biotite: evidence of the magma's high water content. The abundant large white crystals of plagioclase helped make the magma highly viscous.

Andesite Lava

The black crystals in this specimen are the water-bearing minerals amphibole and biotite: evidence of the magma's high water content. The abundant large white crystals of plagioclase helped make the magma highly viscous.

Basaltic Lava

This sample came from a road cut in central Washington, more than 160 km (100 mi) from the fissures where it erupted. The scattered holes were left by gas bubbles in the lava when it solidified.

Cut Pillow Lava

The outer rind of this pillow lava cooled so quickly as it came in contact with cold seawater that it formed a clear brown glass. The interior cooled more slowly, and clusters of dark crystals grew around preexisting minerals.

Pahoehoe Lava

This twisted, ropy surface is typical of pahoehoe (pa HOY hoy), a form of basaltic lava. As fluid lava flowed downhill, a thin skin on top cooled and solidified. It was wrinkled by continued movement of the molten interior.

Pahoehoe Lava

This twisted, ropy surface is typical of pahoehoe (pa HOY hoy), a form of basaltic lava. As fluid lava flowed downhill, a thin skin on top cooled and solidified. It was wrinkled by continued movement of the molten interior.

Pele's Hair and Pele's Tears

Pele's hair forms when wind draws droplets of liquid basalt into strands, like cotton candy. Droplets that break off are called Pele's tears.

Spindle Bomb

Cinder cone eruptions launch clots of basaltic magma into the air, where they may solidify into contorted shapes before falling to Earth. This Paricutín bomb originally had tapered tails on both ends.