What term describes the sheen or gloss seen on the surface of a material?

The term that describes the sheen or gloss seen on the surface of a material is "luster." Luster refers specifically to the way light interacts with the surface of a mineral or material, indicating its ability to reflect light. A high luster implies a shiny or reflective surface, while a low luster may appear dull or matte. It is a key characteristic in identifying minerals and materials, particularly in fields like mineralogy and material science.

While "shine" might seem similar, it does not encompass the broader concept of the quality of light reflection which luster specifically addresses. "Texture" refers to the feel or appearance of a surface or substance, relating to its physical structure rather than its reflective quality. "Clarity" is associated with the transparency or purity of a substance rather than its shininess or reflective properties. Hence, luster is the most accurate term for describing the sheen on a surface.