2-640-592 - © CM Dixon/Heritage Images

Hot Spring and Calcite Formation, Hveravellir, Central Iceland, 20th century. Thermal activity on the lava fields of Hveravellir hot springs, a low temperature area at the northern edge of Kjalhraunnature lava field, a nature reserve on the Kjolur route between Langjokull and Hofsjokull. Calcite is a constituent of sedimentary rock, particularly limestone, much of which is formed from the shells of dead marine organisms.