I've not seen any obvious scratching in my Mr. Aqua low-iron tank but looks like it's possible. Black Diamond lists the Moh's hardness at 6-7. Glass depending on type typically would be in the range of 5.5-7. Low-iron glass appears generally to be toward the middle vs higher end of that. So worst case given those ranges, yes, it could scratch it. Best case at an equal hardness of 7 against 7 then probably so if you really tried. Quartz and silica sand also look to be in the same 6-7 Moh's range so not much difference. One other aspect is that BDBS tends to be more angular in particle shape so I suppose that might make it potentially a little more likely than some other more rounded/polished sand types.