Certain sedimentary rocks such as limestone can be impregnated with hydrocarbons and can contain 4 to 9% bitumen or "shale oil". Asphaltic or bituminous limestone is therefore a mineral impregnated with natural bitumen. This mineral is mined from underground mines or via open-pit mining.
From asphaltic limestone, bituminous oil or asphalt can be extracted for use in the cosmetic or pharmaceutical industry. This tough and sticky product is also mixed with other raw materials to produce the well-known black pavement for our roads. In addition, it is used for waterproofing of roofs, walls, terraces, sidewalks, bridges, casings, tanks, etc. It is also a good acoustic insulator that is able to absorb the noise of machines.
Apart from the mentioned applications, the bituminous oil was once considered a universal remedy, especially good for the treatment of colds, hair loss (Hahn oil), stomach diseases and last but not least, rheumatism. By distillation of asphaltic limestone, it is still possible to obtain gas and petroleum.
On the photo taken of a thin section we see Ooids with bituminous material (containing some fossils) around it. Ooids are spherical or subspherical carbonate grains characterized by an internal concentric structure. Long time ago, the layers or coatings were formed in agitated waters as these grains were rolling around, after which they were piled in layers, under pressure, to form sediment rock.
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