[i]These mystical gems can be purchased with Sensei's credit card. Trade them for various products.[/i]

Pyroxene (青輝石, Pyroxene) are premium currencies in Blue Archive. These are used in Gacha pickups or by other means.

https://bluearchive.fandom.com/wiki/Pyroxene
青輝石 青辉石 청휘석 Pyroxene