There seems to be some confusion regarding the difference between glass and quartz.  In reality quartz is a mineral, glass is man made, sellers who call their items "glass quartz" are usually selling glass items that have been molded and then cut to resemble more valuable carved quartz.  There are many items selling on eBay that purport to be quartz or citrine (a form of quartz) but in reality are glass.  This is expecially the case of  beads, carved pieces and cameos or intaglios.  Make sure you get the seller to put in writing that the piece is natural.  If you have any doubts, check it carefully with a loupe or magnifying glass to see if it has bubbles, one of the easiest ways to spot glass.  Again, there are few real bargains from people who deal in large quantities of quartz, expecially from China, so be sure of your purchase or buy it because you like it, not because it is quartz.