Barite is transparent or whitish transluscent. Its crystals can be like the ones in the photograph, or they can be flakes. The lustre of a mineral describes how it reflects light.
Metals often have a metallic lustre, which means that they're very shiny.
Barite has a vitreous lustre, which means that it looks like glass. Barium is used as a dressing for textiles, as an additive to paper pulp, and in sugar refining.