Historical sketch of Certain Smectite Clays’ Nomenclature

Despite what you may read on other websites, Bentonite and Montmorillonite, are not exactly the same thing.  Montmorillonite was a name coined in 1847 for a discovery near the Prefecture of Montmorillon (départment of Vienne in the region of Poitou-Charentes), France.  [Mauduyt: Un mot sur un morceau de quartz d´une variété particulière, ainsi que sur une substance minérale trouvée dans le department de la Vienne. Bull Soc Géol France 4 (1847) 168-170].  Mauduyt’s chosen name for the mineral, “Montmorillonniste” was short-lived. Monsieurs Damour and Salvetat's suggestion of the label “Montmorillonite” has stuck ever since.

Bentonite proper (aka “Pascalite” http://en.wikipedia.org/wiki/Pascalite), was first discovered in 1830 by the French-Canadian fur trapper Emile Pascal atop the 8600 feet high Big Horn Mountains in Wyoming, but was not distinguished from the former until much later. 

Pascal soon developed a mining partnership with Ray Pendergraft calling the clay after himself.  By the late 1880s William Taylor became the biggest producer of this variety of Smectite in the Rock Creek area of Wyoming, and the common name “Taylorite” was born in his honor.  However, it was just before the turn of the 20^th Century that American geologist W. C. Knight devised the name Bentonite [Eng Min J (1898) 66: 491] for a deposit he found near Fort Benton, Montana^[1]--a portion of the Fort Benton Formation geological stratum that extends into the Rock Creek area of eastern Wyoming.  Pascalite and Taylorite, along with many other names, long since have fallen into synonymy with Bentonite, the preferred name by serious geologists.

Interestingly enough, Fort Benton was originally called Fort Lewis (founded in 1846 as a well-known American Fur Company outpost by Major Alexander Culbertson, but was renamed in 1850 for Thomas Hart Benton.  After military service in the War of 1812, Benton settled in St. Louis, Missouri, and in 1815 and became editor of the St. Louis Enquirer (1818–20).  Noted writer and Democratic Party leader, Benton championed agrarian interests and westward expansion during his 30-year tenure as a US Senator.  As the head of steamboat river navigation on the Missouri River, Fort Benton became a boomtown for gold seekers and cattlemen on their way to California.

[http://www.fortbenton.com/about/]  It later rose to the prominence of a city, and became seat (1865) of Chouteau County.  Fort Benton’s location may be observed about 40 miles northeast of Great Falls, Montana (west central part of the State) at the confluence of highways 80 and 87 and the Missouri River.  By analogy, to stubbornly refer to Bentonite as "Montmorillonite", "Taylorite" or "Pascalite" would be as ridiculous as persisting in referring to Fort Benton as "Fort Lewis".

Over the course of modern history within the US geological discovery process, several other synonyms have been found for what is ostensibly Bentonite.  These include, along with the foregoing Montmorillonite epithets:  Amargosite, Calcium Bentonite, Sodium Bentonite, bentonite magma, Fuller's Earth, hectorite, hormite clay, saponite, southern bentonite, tixoton, volclay, volclay bentonite BC, wilkinite, and Wyoming Sodium Bentonite.

A number of these, such as saponite, have since been segregated from what most would agree to be distinctively Bentonite, but there is still a lot of confusion and misinformation about where to draw the line if at all, between Bentonite and Montmorillonite.  Notice Diatomite is not considered to be in synonymy with either, even though all three are related to “diatomaceous earths”.  The difference is that Diatomite is not a clay.

¹ D.F. Hewett: "The origin of Bentonite" J Wash Acad Sci 7 (1917) 196-198

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