Silk (gemological term)

In gemology, "silk" refers to fine, often fibrous inclusions within a gemstone, particularly common in rubies and sapphires. These inclusions are tiny needle-like structures made of mineral impurities or rutile. The presence of silk affects how light interacts with the stone, often creating a soft glow or chatoyancy (a silky luster effect). While sometimes considered a flaw, silk inclusions can help identify a gemstone's origin and authenticity. Their visibility varies depending on the stone's quality and cut, and they are a natural part of many precious gems.