12mm Glass is strong enough, but glass has a fear of cracking. I'd proceed with caution! Plus, glass resonates at high frequencies - but I wouldn't worry about that too much unless you have a very very resolving high end system.
I've seen an audiophiles high end setup costing 4 lacs around, where the Linn Floorstanders were further isolated on a glass mounted stand with spikes.
should not be a problem on hi-res systems I suppose.
cheers