Wondering what category cubic zirconia fall into? It's not glass, however, really close to a gemstone.
In a way it is a stone it was gem that is ground and heated and re-cut I always think of it as a stone but a very processed one like lazar dyed shape fresh water pearls
" the future belongs to those who belives in the beauty of their dreams"
"They who dream by day are cognizant of many things which escape those who dream only by night." ~ Edgar Allan Poe
Wllaker, technically it is an artificially produced gemstone. It is called a simulant and is made from zirconium oxide powders stabilized with magnesium and calcium. It is definitely not glass which is silica based.
I'd write to them to confirm, but I'd be entering into gemstone category as more correct. Donna