This is a picture of a lava bomb, taken at Jaggar Museum. Lava bombs are fragments that are thrown from a volcanic eruption. If the fragments are larger than 1.5 inches in the diameter are called known lava bombs or lava blocks. It all depends on their shape. Bombs are more rounds and look like blobs of lava.
Blocks are more jagged, and are older.
When they are thrown out from the eruption, they are in a liquid form. Another type of lava is Pele's hair, which are brittle strands of volcanic glass. Lava droplets become stretched in the air, which forms the hair.