Fused (glass) quartz is manufactured by melting naturally occurring quartz crystals of high purity at approximately 2000°C, using either an electrically heated furnace (electrically fused) or a gas/oxygen-fuelled furnace (flame fused). Fused quartz is normally transparent. "Wikipedia"
So - it's glass. And glass is an all time favorite - the colours, the transparency... Soon I will get these lovely briolettes in my mailbox -and who knows? Maybe they end up as jewelry...?...?...?