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bentonite #2


 
     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://infolink.cr.usgs.gov/Photos/MTTownGalleries/FortBentonGallery/InternetFiles/pages/GFdry00.htm   [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:  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.

Chemical formulation, Geological Characteristics
 
Diatomite


     Diatomite in all of its forms, the Bentonites and the alternative Montmorillonoid classification for the broader group, aka Smectite clays, including specifically Montmorillonite, are composed largely of Silicon, once absorbed by diatoms, and originally deposited as sediment.  Some species of diatoms inhabited fresh water, and some in salt water, during different periods of geologic time. [Refer to separate section on diatoms at the conclusion of this article.]  The distinction between Diatomite and the Montmorillonoids is fairly simple.  Diatomite is a form of silica--like a common sand by the same name. Its scientific formula is SiO2 which is also the same basic formula for chert, flint, and common quartz.  However, Diatomite is usually more chalky, and often a fairly homogeneous material found in expansive deposits.  Its SiO2 cousins are more rock-like, and therefore much harder--the result of an extrusive volcanic formation, causing even smaller crystal size.  The diverse forms of Silicon Dioxide are a result of the impurities they contain.  They are mostly found in less impressive quantities than Diatomite, and typically occur in shattered veins, as opposed to sedimentary deposits.

 

     On the other hand, the Silicon absorbed by the species of diatoms making up Montmorillonite and the Bentonites was converted to a “silicate”, specifically an Aluminum silicate (Al SiO4)-4.  As the dead diatoms settled to the lake bottom, their remains became intermixed with considerable detrital material, including other mineral particles, and organic matter.  Hence, the sediment they formed became a powdery clay.  Shales eventually result from and revert to clay, cyclically. As shale eventually is left exposed due to the uplifting of strata during seismic activity, eventual break-up and degradation occurs through mass wasting, weathering, and biochemical interactions, once again contributing to the formation of clay.  If shale is trapped for longer periods under greater pressure, it undergoes a metamorphosis and becomes slate.  Much harder than shale, slate may contain the visible petrified outlines of the remains of animals much larger than diatoms making up its basic infrastructure.  But is ground up slate as effective as living clay in agricultural and nutritional applications?

Various formulae have been proposed for Bentonite, hence the term, “Bentonites.”  One formula for a granular Bentonite from Wyoming is given as:

(Al, Fe1, 6 7'Mg0,33), Si4 O10 (OH) 2Na+Ca++