Of minerals, the ability to reflect light. The quality and nature of the reflection may be a useful diagnostic aid. The term ‘lustre’ is often used in conjunction with the qualifying terms ‘adamantine’, ‘metallic’, ‘resinous’, ‘waxy’, ‘pearly’, ‘silky’, ‘greasy’, and ‘vitreous’. The intensity of the reflection is qualified by descriptions such as ‘shiny’, ‘dull’, or ‘splendent’.