lüster

Lüster, also known as lustre, is a term used in the field of mineralogy to describe the way light is reflected from the surface of a mineral. It is an important characteristic used to identify and classify minerals. The term "lüster" comes from the German word for "lustre," which in turn is derived from the Latin word "lustrum," meaning "to wash" or "to shine."

There are several types of lustre, each indicating different physical properties of the mineral. Metallic lustre is characteristic of minerals that reflect light in a manner similar to metals, such as gold or silver. Non-metallic lustres include adamantine, which is bright and shiny like diamond; vitreous, which has a glassy appearance; silky, which is smooth and shiny like silk; and pearly, which has a soft, iridescent sheen. Some minerals exhibit a combination of these lustres, or may have a dull, earthy lustre.

Lustre can be affected by the presence of impurities or inclusions within the mineral, as well as by its crystal structure and surface texture. It is often used in conjunction with other identifying characteristics, such as hardness, cleavage, and specific gravity, to determine the exact identity of a mineral specimen. Understanding the concept of lustre is essential for mineralogists and geologists in their study and classification of minerals.