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   This particular clay is soft-gray in color, but does not necessarily represent even all of the Wyoming Bentonites, much less Bentonite, globally nor generically.  
     Some producers of Bentonite package it as a product rather than sell it as an ingredient to others, hence such brand-makers can also be called “manufacturers” in that context.  The labels “Sodium Bentonite” and “Calcium Bentonite” in fact, started out as marketing names for Smectite clay minerals from a particular area.  

     It is possible that some “manufacturers” tamper with the formulation of Bentonite by blending, or are not very explicit in stating their formulae, or perhaps are even careless in doing so, as the variety of formulae which follow, may suggest.  In one case the content of Aluminum is omitted which should raise an eyebrow.  
NaO5 Al25Si35O10(OH)2•(H2O)
(Na,Ca) (Al,Mg)6(Si4O10)3(OH)6-nH20
How could such diverse formulations all be Bentonite?  Conversely, with so many different expressions possible, how could anyone intelligently say that Bentonite and Montmorillonite were the same thing?
     What may be said of Bentonite and Montmorillonite is that we seem to have a problem of semantics fed by personal connotations.  If we can agree that the formula for that deposit of basic Montmorillonite, as first described in France, and later analyzed scientifically pursuant to our modern notions of chemistry and geology, can be rendered as:

Al2O3 – 4SiO – x H2O

then we could perhaps exclude the so-called Bentonites, yet admit to the fraternity of technical Montmorillonite that exotic variety claimed by Window Peak Trace Minerals, once formulated as:
MgO Al2O3 5SiO2 nH2O

This logic allows room for a variety of Bentonites to co-exist, and yet be distinguished from Montmorillonite. This would seem to be a sensible approach rather than throwing our hands up in the air and acquiescing that Bentonite is simply the generic name for a whole bunch of “ites”.  Now that we have begun to reconcile a rather confusing pedigree with current geological understanding from marketing practices, how is Bentonite recovered?

Where is Bentonite proper, found?
Bentonite minerals occur as seams or lenses containing up to 50% moisture.  Because deposits are rocklike in nature they are usually extracted by quarrying (opencast mining).
We are informed that most high-grade, commercial, “Sodium Bentonite” mined in the United States, comes from the area between the Black Hills of South Dakota and the Big Horn Basin of Montana.

A great website for the geography of other such locations is: http://www.mindat.org/min-9141.html (This author found only one ambiguous entry, i.e., while the holotype referenced therein evidently came from Wyoming and is referred to as a Fort Benton Shale, one should not infer that Fort Benton is also in Wyoming, but rather recognize that it is in fact in Montana, as previously set forth herein.)

Thus, we see Bentonite as a rather common mineral complex occurring all over the world and at many locations in each of States within the continental USA.  “Calcium Bentonite” is supposedly even more common than the “Sodium Bentonite” variety.  Further, we might infer that a number of the historical locations for Bentonite more accurately were actually for Montmorillonite, and vice versa.

     Historical perpetuation of the apparent confusion seems to have been rampant.  Nevertheless, if a true distinction can be made should we assume Montmorillonite to be any less common?  This author believes that answer to be a resounding, “Yes”.  If we are able to segregate out the Montmorillonites from the broader  group called Bentonites with any kind of consensus, then and only then can we prove this hypothesis.  Another challenge would be to further attempt to grade known deposits according to fresh water formations and those formed under the influence of salt water.  Famous minerals such as limestone and dolomite were definitely formed in shallow marine environments and are much older than the Montmorillonoids.

Alas, such an exercise is not within the scope of undertaking the clarification attempted herein, and the writer leaves it to more highly trained chemists, geologists with the USGS and university professors, professional metallurgists, soil scientists, and the like.  The hypothesis that the two varieties of clay can be more articulately segregated once and for all, satisfying a globally-accepted objective standard, might be the basis for some future