According to the sellers it's sapphire glass. BTW, the Parnis BB homage does come on a bracelet if you are prepared to pay $250 for one.This reminds me of "tiger Concepts" in a way. The crystal is mineral so expect it to scratch. I think the $300 Parnis one is Sapphire. I wish it came with a nice bracelet to.
Corgeut 41mm Sapphire Glass Japan Miyota Men Waterproof Automatic Heritage Watch | eBay