Lava is a liquid with element number 6. It is on the Liquids section.
Lava changes color based on it's temperature. If near solidification point, it is red-orange, becoming more yellow and bright with heat. Every material with the name of "molten [name of material]" is technically lava, with the name of material being it's ctype. Lava itself added from menu cools to Stone.
Lava is used mostly in heating systems, however, Lightning, Plasma and Thermite has mostly replaced it. Lava is born when most of all meltable materials melt (one of examples that do not is Wax). Lava, apart from being hot, is known to light flammable materials on fire.