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Stripped of attributions and many interesting asides, here is a
summary of what posters said. Bentonite:
" . . . [is] a kind of clay used to line landfills . . . ."
#. . . is also used as a clarifier when making home-made wine.  It is
definitely a type of clay.  It bonds to suspended particles and pulls
them to the bottom of the carboy.#
". . . is often used on colon cleansing.  It looks like gunpowder.
The powder itself is often mixed with fiber, apple pectin, and other
roots/herbs.  You add this mixture to juice and drink it down.
Supposedly the concoction pulls out all the old stuff that's
clinging to the walls of the intestines.  You have to drink a ton of
water on it."
". . . is a clay that is used for a number of industrial purposes.
It also has a number of food industry uses.  Bentonite is a VERY
commonly used thickening agent in a wide variety of food products (
Fast Food "shakes" comes to mind, they call them shakes because there
is NO milk in them, just ice and thickeners and flavorings).  You have
probably eaten it for years without realizing it. The good news is,
since it is mineral based it is GF!  So don't worry if you see it on
an ingredients list."
". . . kills insects and some parasites because its particles are so
small and SHARP.  This is the reason some take it as a supplement:
to get rid of parasites.   Since gluten is a protein (and vastly
smaller than any parasite, bentonite would have NO effect on it.   If
it worked by simple absorption enough to get all the gluten it would
dry your internal tissues and damage them (like the "dry cotton roll"
burn you get in your mouth if the dentist forgets to wet the roll
before he/she puts it in.)"
". . . is a clay, specifically one that forms from buried layers of
volcanic ash.  It is a mixture of minerals that swell and expand as
they absorb water, and which can also retain certain kinds of ions
well. Many of the "badlands" in the West are there because of
bentonite-rich soils; the clay resembles popcorn when dry and doesn't
allow much vegetation to take hold.
. . . [Its] swelling behavior makes bentonite good to seal landfills.
. . . [It's] quite harmless in small doses, because the way we
geologists identify a bentonite layer in the field is to take a small
piece and chew it; it's plastic, almost like chewing gum.  Traditional
Navajos use small amounts as a remedy for diarrhea (they call it
"hashtl' ish" or "dleesh," or white clay).  Putting a lot of it in
your gut would probably be uncomfortable at the least!  It would
retain water, but I don't know about gluten. The "kao" in Kaopectate
is (or was) kaolinite, which is another type of clay: one that does
not appreciably swell when absorbing water."
"According to " A Consumer's Dictionary of Food Additives," . . . is:
'A colloidal clay (aluminum silicate) that has a high swelling
capacity in water.  Used as a food additive, as a thickener, and as a
colorant in wine.  Poison if given by vein, causing blood clots, and
may cause tumors.' "
". . .[is] a clay-like mineral that supposedly clears toxins out of
the human system. The book Nutritional Healing recommends it
(really!) when fasting and for clearing the system of things like
anasthesia after surgery. I bought the bottled product by Yerba at a
health food store, before a recent surgery. It's the only clay
supplement that I've found that doesn't include other "cleansing"
herbs, many of which I react to."
"About the Bentonite helping gut problems, last week my doctor
reminded me that the health store product "Sonne's #7" (which is
bentonite in suspension) would probably be useful.  He was right.
I'd used it off and on for many years, but not since the cd
diagnosis.  The pain and spaciness went away quickly."
". . .[is there] aluminum in bentonite[?]  There is plenty. Bentonite
is a mixture of clay minerals, principally montmorillonite (a hydrated
aluminum-magnesium silicate), which can contain up to about 13%
aluminum by mass.  But the real question is whether this Al is
bioavailable or not -- it might just pass right on through."

Hope I didn't miss any.
Bobbi in Baltimore