Quartz is very safe; it's silica. The worst you have to worry about is other compounds mixing in, but those all look pretty good. Microcrystaline quartz is what a lot of aquarium safe rock consists of, though it doesn't look like quartz per se.
I find the larger white quartz structures kind of tacky; too reminiscent of plastic gem stones and resin cast ornaments that bubble. It can be done to look good, but it's tricky.
The one in the middle looks good. Do you have more like it? Odd groups of stone tend to look good.
I like the second driftwood setup. I like the uncut "jaggedness" of the third quartz pic.
Maybe try to get a few of them kind of protruding from the substrate so that it looks like they are forming in the tank. Of course, I have no idea what that would look like as I have no experience in doing so, just a thought.