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Ruby Essentials

Inclusions in Rubies

Rubies have long commanded heavy interest and brought high prices when they are natural and untreated. In fact, the popularity of rubies was a critical component for those involved in the industry to develop color and clarity treatments. Innovations in types of treatments have helped satisfy a widespread demand for rubies, but have also led to confusion about clarity standards in natural , untreated rubies.

sunrise ruby sothebys
The eye-clean Sunrise ruby in a custom setting designed by Cartier. Photo credit: Sotheby’s.

All natural and untreated rubies will have some degree of inclusions present. Even the best quality stones will contain inclusions, which is why the most desirable clarity grade for rubies is considered to be “eye-clean,” which means no inclusions will be visible to the unaided eye.

Why Is Understanding Ruby Inclusions Important?

Studying inclusions in rubies gives gemologists an understanding of the gemstone’s origin and treatment history. Each inclusion will also contribute in different ways to the sparkle, color, and brilliance of the stone.

inclusions in ruby
Visible liquid inclusions and mineral included crystals seen in a natural ruby gemstone.

One thing to always consider is that natural gemstones will be far more valuable, durable , and rare than any synthetic, and natural gemstones will carry inclusions. When considering a ruby, it is always best to weigh the type, number, and placement of inclusions to determine the long term value and beauty.

Typical Ruby Inclusions

Cavities

These are voids or holes that extend from the surface of the gemstone into its interior. There is also a very common treatment that is aimed at diminishing the appearance of this inclusion called cavity filling. This process involves using color-infused glass injected into the cavity to fill cracks and fissures.

color zoning ruby gemstone
An example of slight color zoning in a ruby gemstone.

Color Zoning

This term refers to areas or bands of alternating color in a gemstone. Color zoning occurs naturally during crystal formation and is often most apparent in the crystal rough.    

Fingerprint Inclusions

These are networks of tiny liquid-filled tubes that resemble human fingerprints.  Fingerprint inclusions are possibly some of the most common for rubies being formed when rubies re-crystallize to partially heal a fracture zone. These inclusions tend to be small in nature, especially to the naked eye, and are not likely to negatively impact quality.

inclusions ruby gemstone
Mineral included crystals seen in a natural ruby gemstone.

Halo or Discoid Fractures

These are oval or circular fractures surrounding a solid or liquid inclusion that resemble the look of a fried egg.  Stress due to the radioactive decay of tiny zircon crystals aids in forming these fractures, but they can also be the product of high temperatures required for heat treatment.

Mineral Included Crystals

These inclusions are the result of light, dark, transparent , or opaque minerals being trapped inside a gemstone. In ruby, you can frequently find minute crystals of pyrite, garnet, zircon, calcite, and spinel, for example.

Liquid Inclusions

These are liquid-filled spaces within a gemstone. In the mineral species corundum formed from a metamorphic origin, carbon dioxide presence as liquid inclusions is an indication that no heat treatment has been used since that process would mask these inclusions.

silk rutile inclusions in rubies
Silk rutile inclusions in a ruby seen under magnification.

Silk

This term refers to the fine rutile needles that create the sleepy transparency of some rubies.  They appear in groups or pockets. Silk is also responsible for asterism in star rubies. Silk is an example of an inclusion type that could enhance the value of a ruby.  In small amounts, the highly reflective rutile needles cause light to scatter within a cut ruby. This process will then illuminate a stone’s darker facets and enhance its brilliance.

Just as certain inclusion types can indicate a particular origin location, many have attributed levels of inherent quality based on the region where a ruby is found. On the following page, we unravel the truth behind the connection between Ruby Rarity & Enduring Value.

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