Several types of inclusions are found in sapphires. Among these are long thin mineral inclusions called needles that develop inside the gemstones as it is forming. Fine needles are called silk when they occur as the mineral rutile in intersecting groups. Not all sapphires contain silk. Silk is an example of an inclusion that may actually add value to a sapphire. In moderate amounts, the highly reflective rutile needles scatter light within a cut sapphire, helping to illuminate a stone’s darker facets and enhance its brilliance.