lusterless

Lusterless refers to the absence of luster, which is the quality of being glossy or shiny. In the context of minerals, lusterless describes a mineral that does not exhibit any reflective or glossy properties. This can be due to several factors, including the mineral's composition, structure, or the way light interacts with its surface. Lusterless minerals often appear dull or matte, lacking the characteristic shine that is typical of many other minerals. Examples of lusterless minerals include graphite, talc, and some forms of clay. The absence of luster can be an important diagnostic feature in mineral identification, as it helps to distinguish between minerals with similar physical properties but different compositions.