RE: nutrient diffusion into vermiculite

>From: Stephen.Pushak at hcsd_hac.com
>> From: Charley Bay
>> As an aside--how come nobody ever mentions "pearl-ite"?
>Don't have any information on it. I don't know if it has the layer
>structure that vermiculite has so crushing it up to remove trapped
>air (buoyancy) probably gets dust instead of tiny flakes. Anybody
>know anything else about it?

From my younger days, when my father was in the non-metallic mining 
business, I remember perlite as a very light, fluffy form of pumice. It 
is, I think, essentially SiO2 puffed into a glassy foam in volcanic 
structures. This would give it a fairly high surface area, but nothing 
like the mica leaf structure of vermiculite. It also would be very 
difficult to keep sunken, for the internal bubbles are not all 
connected to the surface. Crushing would produce finely powdered glass 
dust. Not quite as bad as asbestos, it would be something you certainly 
don't want to breathe.

Vermiculite can be boiled, like peat, to easily make it sink. It's just 
mica with enough initial water between the leaves to puff up when baked 
quickly. It's not really a clay, and comes from the ground in large 
flat sheets, just like any mica. Chopped fine and flash-baked, it has 
the same high surface-area-to-volume ratio that is characteristic of 
the more microscopic structures of clays, but comes in bigger lumps so 
water can move thru it easier. I believe that vermiculite is primarily 
aluminum silicate, like many clays, with (perhaps) a different water of 
hydration giving it a slightly different structure. Don't count on my 
memory for perfect accuracy on these topics, but that's the way I 
remember this stuff from over 40 years ago. :-)