Luster describes how light reflects off the surface of a gemstone. It can range from:
* Metallic: Reflecting light like a polished metal (e.g., pyrite)
* Adamantine: Brilliant and sparkling, like a diamond (e.g., diamond, zircon)
* Vitreous: Glassy and shiny (e.g., quartz, amethyst)
* Resinous: Like the surface of resin (e.g., amber)
* Pearly: Soft and iridescent, like a pearl (e.g., opal)
* Silky: Having a silky, fibrous appearance (e.g., moonstone)
* Dull: Reflecting little light (e.g., some opals)
The way a gemstone reflects light can dramatically impact its perceived brilliance, sparkle, and overall attractiveness. Luster, alongside hardness and other factors like color and clarity, all contribute to a gemstone's beauty and value.