Carbonatite, Oldoinyo Lengai, Tanzania: Due to its low temperature (just over 500°C) the molten lava appears black in sunlight, rather than having the red glow common to most lavas. It is also much more fluid than silicate lavas, often less viscous than water. The sodium and potassium carbonate minerals of the lavas erupted at Oldoinyo Lengai are unstable at the Earth’s surface and susceptible to rapid weathering, quickly turning from black to grey in colour. The resulting volcanic landscape is different from any other in the world. (© Thomas Kraft, Kufstein, via Wikimedia)
