Quote
Isildur
Some googling turned up that quartz weighs 2643 kg / m^3.

Interestingly, steel is 7850 kg / m^3.

Leather is supposedly 945 kg / m^3.

Though, one could argue that in order to be effective as armor glass would need to be thicker than steel. I think it's technically harder than steel, but much more brittle. So if you want your leggings not to shatter the first time someone hits them with a metal sword, the glass would have to be fairly thick.

Glass is not quarts. The density of glass changes depending on its composition. Flint glass used for making eye glasses for example use to be made from a composition of primarily silica and lead. Such compositions can have a density greater then iron depending on the percentage of lead that makes up the final compound . My point being that armor made from it would not even need to have as much total material to have a mass greater then more tradditional armor making materials.