Coloured scanning electron micrograph (SEM) of a particle of Saharan dust. Such mineral particles, measuring 0.1 to 50 micrometres, often travel for vast distances on the wind. A high iron content gives it its reddish colour. Due to the proportion of nutrients such as calcium and magnesium, Saharan dust plays a role in enriching soils. For example, 40 million tons of Saharan dust reach the rainforests of the Amazon every year, and dust from the Sahara also makes an important contribution to atmospheric fertilization on the Iberian Peninsula. The dust can also cause algal blooms in the oceans. Magnification: x13,000 when printed at 15 centimetres wide.