[muawiyah]

The silica also points to the envelopes having been filled by the terrorists outdoors on a slightly windy day, most likely at a picnic table in Sugar Sand park in Boca Raton.

Remember, it wasn't a uniform mixture ~ different samples had different silica content.

Simply cleaning the bacterial mat of debris and producing spores "weaponizes" anthrax quite nicely.

[piasa]

I don't think sugar sand is entirely composed of silica... most of it is ground up calcium since it's made of coral, not minerals from the mountains like say, the sand in Virginia. You'd need to dissolve it in some acid to remove the calcium and that may still leave other minerals.