Detail of Basalt, from Kilauea volcano, below East Rift zone, Hawaii, United States of America.
This ropey lava was very runny when hot (1100°C) and was able to flow in these smooth bands. It is known as pahoehoe, from the Hawaiian word meaning smooth, unbroken lava.
Image: Benjamin Healley
Source: Museum Victoria
Basalt, Woodend, Victoria, Australia.
Basalt lava forms during melting in the mantle. It cools quickly so its crystals are very small, giving it a fine-grained appearance.
Source: Museum Victoria
Pumice, picked at sea, 1315 miles from Java Head.
Pumice contains so many air-filled cavities that it actually floats.
Source: Museum Victoria
Scoria, quarried on The Anakies, Victoria, Australia.
Source: Museum Victoria
Andesite, Thíra Harbour, Greece.
Source: Museum Victoria
Lavas with the same composition can look different. For example, basalt can be very dense or light and full of gas bubbles (as in scoria). Rhyolite can consist mainly of glassy fragments (ignimbrite), or solid glass (obsidian), or frothy glass that is light enough to float (pumice).