Inclusion

from the Antique Jewelry University

A slender, double refractive, crystal of unknown composition causes a beautiful image when it's host, a garnet, is placed in between crossed polars. Image by Tim Spauwen
A slender, double refractive, crystal of unknown composition causes a beautiful image when it's host, a garnet, is placed in between crossed polars. Image by Tim Spauwen
An internal feature in a gemstone. Often microscopically small. The term inclusion usually refers to foreign materials in gemstones like guest crystals, fluids and gasses but are sometimes used to describe phenomena that don't comprise foreign substances such as color zoning, twinning and phantoms.

Inclusions can end up in gemstones in several ways:

  • they have formed prior to their host (protogenetic) which grew around them like a garnet crystal in a diamond,
  • they have formed together with the host (syngenetic) like rutile in corundum,
  • they have formed after the host developed (epigenetic) like fingerprints in rubies.
This zircon crystal in a sapphire gives away that it's host has been heated by showing us a stress fracture around it Image by Tim Spauwen
This zircon crystal in a sapphire gives away that it's host has been heated by showing us a stress fracture around it Image by Tim Spauwen

The internal world of gemstones is of great value to gemologists who can derive a lot of information from observing inclusions. The presence or absence of some inclusions can act as diagnostic clues for those that know how to interpret them.

Edward Gübelin and John Koivula are two gemologists that have published three books on inclusion studies that every gem fanatic should have read: the Photo Atlases of Inclusions in Gemstones.

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