you know I have the same problem with little sand piles under the dash. maybe this car was blasted already?
as far as alluminum oxide being the second hardest blasting media goes, I dont think thats right. reason I say is thats what I use when re-finishing firearms and cleaning rust off of small parts. I was told that the A/O is pretty soft and not to use anything else on areas where the metal is to be exposed and subject to visual inspection. I may be wrong but I don't think its that harsh. I'll gho look it up and see though.