Which mineral exhibits a shiny luster and is often used as a lubricant?

Mica is the correct choice because it is characterized by its shiny luster and layered structure, which allows it to easily split into thin sheets. This property makes mica an effective lubricant, as the sheets can glide over one another with minimal friction. The shiny appearance of mica, especially in its common forms like muscovite and biotite, contributes to its aesthetic qualities, making it a popular choice in various applications such as cosmetics, electronics, and as a lubricant in different industrial processes.

While biotite is a type of mica, it does not have the same widespread use or the same level of shiny luster as muscovite, the more commonly recognized form of mica. Feldspar, on the other hand, lacks the same shiny luster and is primarily used in ceramics and glass-making. Calcite, while it exhibits some luster, does not have the lubricating properties that mica possesses. Therefore, mica stands out as both visually appealing due to its shine and useful because of its lubricating characteristics.