Little School of Mineralogy 13 – interesting facts about nitrates and the sediment called caliche
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Little School of Mineralogy – 13
Interesting facts about nitrates and the sediment called caliche
Did you know that natural nitrate deposits were very important in the past?
Nitrates are essential for two human activities – agriculture and warfare. If we enrich soil with a mixture of nitrates, potassium and phosphates, plants grow much better on it.
On the other hand, if nitrates are mixed with charcoal and sulfur, a black explosive substance is formed – gunpowder.
Because nitrates are soluble in water, they occur very rarely in nature. Therefore, there are only two natural sources of nitrates. The first source is guano deposits, earthy or hard masses formed by the decomposition of bird and/or bat droppings.
The second source is the desert sediment caliche in the South American Atacama Desert, which is rich in nitrates. It is therefore not surprising that wars were once fought for control over nitrate-rich areas, which ultimately also influenced the outcome of wars.
Without supplies of Chilean caliche, the Allies probably would not have won the First World War.
What is caliche?
Caliche is a sedimentary rock that can be described as hardened natural cement, most commonly composed of calcium carbonate, which binds other materials such as clay, silt, sand and gravel.
However, the term caliche is also used for deposits of nitrate salts such as those found in northern Chile and Peru. The name caliche is Spanish and derives from the Latin word calx, meaning lime. The terms calcrete and kankar are also known alongside caliche.
Caliche is most often light in color, ranging from white and pale pink to reddish brown, depending on the presence of impurities.
It most commonly appears on or near the surface, and the thickness of a caliche layer varies from a few centimeters to several dozen centimeters, with several caliche layers sometimes occurring in the same place.
Where and how does caliche form?
Caliche forms in areas with an average annual temperature above 5 °C and annual precipitation of less than 650 mm per square meter.
The process of carbonate caliche formation is very complex, and besides temperature and precipitation, plant roots also play a very important role in its formation because they release carbon dioxide.
Caliche can also form through capillary action. In an arid area such as the Atacama Desert, rainwater sinks very quickly into the soil.
Later, as the soil surface dries, water located in the lower layers begins to rise by capillary action, bringing dissolved mineral substances with it. Then, as the water evaporates, mineral substances are deposited near the soil surface.
Did you know that the famous Croatian explorers, the Seljan brothers, explored nitrate deposits in the Atacama Desert?
The famous Karlovac-born brothers Mirko and Stjepan Seljan directed their adventurous exploratory spirit toward ethnological and natural history research in distant regions.
They first set out on an expedition to Africa in 1899, where they mainly focused on exploring the area of then Abyssinia, today’s Ethiopia, and after that they traveled to South America.
During exploration ventures that included the Paraná River area, the state of Mato Grosso, the course of the Aquapehe River, the route from the Salto Grande waterfalls on the Paranapanema River to Paraguay’s capital Asunción, and numerous other regions, the Seljan brothers spent part of their time researching Chilean saltpeter deposits in the Atacama Desert.
Prepared by Biserka Radanović-Gužvica.