Jet is a type of lignite, a precursor to coal, and is a gemstone. Jet is not a mineral, but rather a mineraloid. It has an organic origin, being derived from decaying wood under extreme pressure. This t-shirt is organic certified cotton, so not a mineraloid, but it does share the same colour as jet.
It is also available in green, blue and bruised white, but we couldn't come up with as good colour descriptions for those three.
A Jet Grey base with a darker CHPT3 logo. Made from soft 100% organic certified cotton and with the logo printed with environmentally friendly water-based ink. Only available from CHPT3.com