Does it sparkle when smoke it? If so, fiberglass, makes it way more and cuts your lungs making the THC go directly into your bloodstream making you think its better weed. If it does not sparkle, might be silica flakes, again with the makes it weigh more but does not make it sparkle or make it seem better, just weighs more. The thing with the silica is if a piece goes through everything else and gets into your lungs, you can get a mesothelioma like condition, YAY GOOD DRUG DEALERS!!!!.........