DNA extraction from Vermiculite - (May/15/2014 )
Well as you said it's a mineral (and not organic), so why do you expect DNA there? If it was used as a substrate already i.e. there is "contamination" with soil and/or it's life forms then you might find DNA...
Clays in general are extremely strong cation exchange compounds - so cations are probably being sequestered from the buffers and hence stopping the DNA being salted out on the addition of alcohol. I don't have any ways of stopping this - but you could try searching for clay DNA extraction.
if there's really DNA it might be bound itself to the vermiculite too quite strongly...check e.g. this:
Do you have DNA or cells in the vermiculite? If you have cells, better try a cell detachment and concentration protocol before doing the DNA extraction.
There are several methods for cell detachment and the efficiency may depend on the species to detach. Probably the most reliable method to quantify would be FISH or CARD-FISH on the attached cells and counting them under CLSM but it is tedious, time consuming, needs specific equipment, chemicals and probes, and some experience with the CLSM.
Try with the protocol in Kallmeyer, J. et al., 2008. New cell extraction procedure applied to deep subsurface sediments. Limnology and Oceanography: Methods, 6, pp.236–245. I used a modified version for some samples from acidic environments that were resistant to other methods including few soil kits, and it was the only way I could get DNA good enough.