The term Bentonite refers to a rock, precisely to a clay, generally made up of minerals from the smectite group and in particular from montmorillonite. Sodium montmorillonite smectites are the most valuable and can contain up to 90 % of useful minerals. The most important deposits derive from argillification processes of volcanic precursors deposited in a marine or lake environment.
The main component is montmorillonite which other clay minerals (illite, kaolinite, etc) are associated with as well as residual minerals such as: quartz, feldspar, calcite, biotite, opal, cristobalite and also zeolites. The presence or absence of these components explains the great variety of extracted bentonite, whose remarkable diversity can influence the quality of the mineral and therefore industrial applications.
The first bentonite deposit was discovered around 1890 in Wyoming, Montana, near Fort Benton, the place that gave its name. The United States is the world’s leading producer, followed by China, Turkey, Greece and India. The main Italian deposits are in Sardinia and Puglia. Extraction is usually done in open-cast quarries.