What Are Inclusions?
Sapphires host many different inclusions, and even the best stones are not expected to be inclusion free.
A sapphire with no inclusions is often viewed with suspicion; it may be a synthetic stone or a glass imitation. The best clarity grade for sapphires is “eye-clean,” which means no inclusions are visible to the naked eye. When evaluating the clarity, experts consider the size, number, location, and overall visibility of the inclusions. Inclusions are a natural consequence of crystal growth. Sapphire inclusions vary with their source or origin and treatment history.
Inclusions typically found in sapphires include the following items:
Cavities – voids or holes that extend from the surface of a gemstone into its interior.
Color Zoning – areas or bands of alternating color in a gemstone.
Concaves/Naturals – natural indentations in the surface of a gemstone created during crystal formation. These growth marks are usually found on the girdle and do not affect the gemstone’s beauty or luster.
Feathers – small inclusions that have the wispy appearance of a feather.
Fingerprint Inclusions – networks of tiny liquid-filled tubes that resemble human fingerprints. Fingerprint inclusions are formed when sapphires re-crystallize to partially heal a fracture zone.
Halo or Discoid Fractures – oval or circular fractures surrounding a solid or liquid inclusion. These are formed from stress due to the radioactive decay of tiny zircon crystals or from the high temperatures required for heat treatment.
Included Crystals – light, dark, transparent or opaque minerals trapped inside a gemstone. In sapphires, you can frequently find minute crystals of hematite, zircon, spinel, calcite, and mica, for example.
Liquid Inclusions – liquid-filled spaces within a gemstone.
Silk – the fine rutile needles that create the sleepy transparency of some sapphires. Silk is also responsible for asterism in star sapphires. 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.
Besides color and clarity, which are natural to the stone, the man-made Cut of the stone can also effect it’s value.