Many would think this an easy characteristic by which to identify minerals, but it is one of the most deceptive. Minerals can have a range of compositions in their make up, and this variation in composition can cause color variations as well. The common mineral quartz illustrates this very well. It comes in a wide range of colors, including smoky, pink, clear, opaque and purple. This property refers to the mineral's appearance when light is reflected off its surface.
Some minerals give off a very shiny appearance, while others appear very dull.
A broad range of adjectives are used to describe a mineral's luster. This property also relies on the mineral's color, but it is far more consistent in mineral specimens and does not vary within a mineral series. Streak is tested by scratching the surface of a porcelain plate with the mineral to obtain a powder residue. The color of the powder becomes an important factor in determining which mineral the mineralogist is dealing with.