Basalt is an effusive rock of volcanic origin produced by the solidification of lava on the earth’s surface, and is generally black or in any case dark. Composed of calcium plagioclase, pyroxenes and gabbro, it is characterised by an appearance ranging from prolific to microcrystalline or glassy.
But what exactly does it consist of? Where is it found? And what are its most important features? Here’s what you need to know about Basalt.
What are the characteristics of Basalt?
Basalt is created by the solidification of magma in contact with air or water, and is the main rock found on the upper part of the oceanic crust.
Its name derives from the late Latin “basaltes”, which means “very hard rock”, although the origins of the term probably date back to the Egyptian language. It was then Georg Agricola in 1556 who used this word to identify the black volcanic rock we know today with this name.
Basalt is classified according to the regulatory minerals it contains and the saturation and sub-saturation levels. The types of Basalt known to us are:
- Tholeiitic basalt: that of the oceanic ridges, which constitutes most of the ocean floors and, whose evolution leads to increasingly over-saturated products.
- Olivinbasalt: intermediate form and rich in olivine, whose evolution can lead to both saturated and supersaturated products.
- Basanite: a nephelin-normative basalt whose evolution leads to increasingly undersaturated products.
Basalt is the constituent rock of the largest magmatic provinces, including the Deccan Plateau in India, the Columbia Plateau (United States) and the Hawaiian Islands. In Italy, however, it is found in Aci Trezza, Sicily, Sardinia and the Aeolian Islands. Finally, it is present in most ocean bottoms.
Basalt is widely used for the construction of crushed stone for railway embankments, grit for the production of asphalt, but also for slabs, steps, road edges, fireplaces, statues, floors and, in general, street furniture.
What are the colors of the basalt?
Basalt is typically black or in any case of dark colour, due to the characteristics of the magma from which it forms. Depending on the area in which it is extracted, it can have more or less grey nuances and shades.
What are columnar basalts?
We have already seen how basalt is the result of the solidification of volcanic magma. Often, during the cooling phase, there is the formation of joints and fractures due to the forces that tend to significantly contract this material, leading to a horizontal fracture.
These extensive fractures, whose diameter depends on the cooling rate of the magma, are at the base of the columnar basalts that are often confused with the work of man: an example is the Giant’s Causeway in Northern Ireland (see picture above) or the Vogurviti cliff, north of Blonduös, Iceland.
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