Lava is molten rock material that reaches the Earth’s surface through volcanic vents and fissures; also, the igneous rock formed by consolidation of such molten material. Relatively rapid cooling at the Earth’s surface may transform fluid lava into a dense-textured volcanic rock composed of tiny crystals or glass or both.
The temperature of liquid lava ranges widely but generally does not exceed 1200°C. Basaltic lavas are usually hotter than rhyolitic ones. The viscosity of lava depends largely upon the temperature, composition, and gas content.
As lava cools, it becomes more viscous and the rate of flow decreases. Rapid cooling, as at the surface of a flow, promotes the formation of glass. Slower cooling as near the center of a flow, favors the growth of crystals.
During many volcanic eruptions the lava is so rapidly ejected that it is blown to bits by the explosive force of expanding gases. The small masses rapidly congeal and settle to the Earth to form thick blankets of volcanic tuff and related pyroclastic rock. Lava flows and volcanic tuffs cover large areas of the Earth’s surface and may form more or less alternating layers totaling many thousands of feet in thickness.
Lava is also a name given to ceramic material used for molding gas-burner tips, electrical insulating parts, nozzles, and handles. It may be calcined talc, steatite, or other material. It is molded from magnesium oxide, and it is hardened by heat treatment after shaping and cutting. It is baked at 1093°C. The compressive strength is from 138 to 207 MPa. It will resist moisture and has high dielectric strength. Rods as small as 0.05 cm in diameter can be made. Alsimag is the trade name of lava that is produced from ground talc and sodium silicate.
