Quality of bentonite material is primarily dependent on the geology of the exploited bentonite deposit. The deposits are typically formed as a result of ash flows of volcanic eruptions, depositing as tuff layers. Smectites form when the tuff reacts with water in low temperature (diagenetic to low-temperature hydrothermal-) conditions in the presence of excess alkali (e.g. Drief etc al. 2001). Increasing temperature of formation promotes the formation of mixed-layer smectite-illite clays. Parent rocks of bentonites are mostly acidic to intermediate tuffs. Alteration of mafic parent material produces iron-rich bentonite (Christidis 2006). Sedimentary bentonite formations are typically stratified, with different layers possibly originating from different volcanic events. Compositional variation between layers thus occurs, while a single layer may be thick and wide-ranging. Detailed geological mapping including stratigraphic information provided by the producer would support the user inmaking its own estimates on the quality and homogeneity of the supplied material.
states. About 25 different mining operations are active, and 14 plants are processing bentonite. The northern Rocky Mountain-High Plains region has lead the world in high swelling or Wyoming bentonite. The major producing centers are widely located in Wyoming, Montana, and South Dakota. Nearly all the bentonites in this region occur in sedimentary formation of Cretaceous age. In Mexico, bentonite is produced mainly from 2 centers, Pueblo and Monterrey. There are other bentonite deposits, and a few have been mined on a small scale. Other producing countries in North America include Argentine, Brazil, and Peru.
Geologically, bentonite is a bed of altered volcanic ash. One of the biggest deposits of this volcanic ash occurred over 60 million years ago in areas of North America now known as the Blacks Hills of Wyoming and South Dakota, and the Big Horn Mountains of Wyoming.Bentonite clay mined in Wyoming actually comes from this volcanically deposited bentonite bed. Bentonite clay mined in other areas of the world may be from other types of geological deposits. Because of their small particle sizes, clays and clay minerals are analyzed with special techniques such as x-ray diffraction, infrared absorption and electron microscopy. Cation Exchange Capacity (CEC), water adsorption and surface area are some of the properties of clay minerals that are often determined in order to better characterize clay minerals as well as to minimize drilling problem. Bentonite is plastic clay generated frequently from the alteration of volcanic ash, consisting predominantly of clay minerals, usually montmorillonite. Depending on the nature of their genesis, bentonites contain a variety of accessory minerals in addition to montmorillonite. These minerals may include quartz, feldspar, calcite and gypsum. The presence of Propast - Dobrovoletz bentonite deposit is discovered in 1960. Its operation starts in 1963. The bentonite form the Propast - Dobrovoletz deposit is of hydrothermal – metasomatic type. They are related to Oligocene volcanogenic – sedimentary complex witch belongs to the first intermediate pyroclastic horizon. The deposit is located eastern of Kurdjali town. The bentonite clays are formed in hydrothermal alteration of volcanic tuffs. They alternate by not altered tuffs in some areas in or around the deposit. The products of the second acid lava – pyroclastic horizon, cover the bentonite clays.The clays are green, gray - greenish and yellow -greenish. They contain apatite, biotite, plagioclase, etc. The main mineral is montmorilonite (Na - montmorilonite type). The caolinite is in minor amounts. Statistical data on the world production of bentonite, fuller’s earth, and kaolin are compiled by the US. Bearue of Mines (Ampian and Polk, 1980). According to them the world production of bentonite is in 1980 was 7,625,204 tons of which approximately 1.5 million tons is produced in the United States. The total kaolin production in 1980 was estimated 22,971,000 tonnes of which approximately 13 million short tons was produced in the United Sates and the United Kingdom combined. World production data on other clays are not available through published literatures. In 2005, U.S. was the top producer of bentonite with almost one-third world share followed by China and Greece, reports the British Geological Survey.
The absorbent clay was given the name bentonite by Wilbur C. Knight in 1898—after the Cretaceous Benton Shale near Rock River, Wyoming. Other modern discoveries include montmorillonite discovered in 1847 in Montmorillon in the Vienne prefecture of France, in Poitou-Charentes, South of the Loire Valley. Most high-grade natural sodium bentonite is produced from the western United States in an area between the Black Hills of South Dakota and the Bighorn Basin of Wyoming. Mixed sodium/calcium bentonite is mined in Greece, Australia, India, Russia and the Ukraine. In the United States, calcium bentonite is primarily mined in Mississippi and Alabama. Other major locations producing calcium bentonite include Germany, Greece, Turkey, India and China. It should be noted that in some countries like the UK and US, calcium bentonite is known as fuller's earth, a term which is also used to refer to attapulgite, a mineralogically distinct clay mineral but exhibiting similar properties.
World Production of Bentonite (By Principal Countries)
| Country | 2005 | 2006 | 2007 |
| World total production | 14400 | 14800 | 15700 |
| Brazil | 460 | 419 | 330 |
| China | 2300 | 3200 | 3200 |
| Germany | 352 | 364 | 385 |
| Greece | 1125 | 1100 | 1100 |
| India | 590 | 610 | 630 |
| Italy | 446 | 470 | 560 |
| Japan | 422 | 425 | 425 |
| Mexico | 426 | 435 | 614 |
| Russia | 500 | 456 | 460 |
| Turkey | 583 | 400 | 400 |
| USA | 4710 | 4940 | 5070 |
| Other countries | 2486 | 1981 | 2526 |
Source: World Mineral Production, 2003-2007
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Reported Consumption of Bentonite, 2005-06 to 2007-08
(By Industries)
| Industry | 2005-06 | 2006-07 | 2007-08 |
| All industry | 126000 | 125600 | 124700 |
| Alloy steel | 900 | 900 | 900 |
| Ceramic | 700 | 700 | 700 |
| Chemical | 1500 | 1500 | 1500 |
| Ferro-alloys | 500 | 500 | 500 |
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