Luster is how shiny the mineral is. Some can be glassy. Others can be silky, dull, or metallic. Silky minerals such as gypsum have a smooth appearance. A vitreous mineral is usually clear, like glass, and describes minerals such a quartz. There are at least ten kinds of luster to describe how the mineral's surface looks. Below is an image of satin spar gypsum, a silky mineral.