The lava takes on different forms depending on what happens as it erupts. Here are some examples.
There are "volcanic bombs" ranging in size from 1cm to 1m in diameter.
They often have a solid basalt spindle shaped case, with a centre of green olivine crystals. They may be solid lumps of basalt of a particular temperature (about 1000 deg C) when ejected but spinning formed the shape and the olivine crystallized as they cooled.