natural ruby inclusions

Gemologists can use magnification to determine if a ruby has been treated, by the types of inclusions.

​Below is a list of inclusions found in natural rubies.

untreated rubies

mineral crystal


​Unaltered mineral crystal inclusions such as rutile, calcite, and apatite, to name a few.

straight / angular growth


​Straight, angular, or even hexagonal growth banding with distinct, sharp lines.

silk

Intact, intersecting rutile needles in a natural, untreated ruby
Photo courtesy of GIA

​Intact, fine, needle-like rutile inclusions intersecting at 60° angles in the same plane, known as "silk".

fingerprint

Inside a natural, untreated ruby is this fingerprint inclusion made up of thousands of microscopic liquid inclusions.
Photo courtesy of Scott Papper, GIA GG, AJP, CM (NAJA), Global Gemology & Appraisals

​Networks of microscopic, liquid inclusions that resemble a human fingerprint.

heat treated rubies

discoid fracture


Oval or circular tension halos surrounding an included crystal that expanded during heat treatment, causing a fracture in the ruby.

partially healed fingerprint

Partially healed fingerprint in a heat treated natural ruby
Photo courtesy of Scott Papper, GIA GG, AJP, CM (NAJA), Global Gemology & Appraisals

When exposed to high temperatures, the networks of tiny, liquid-filled tubes begin to resorb.

sintered surface areas


Sintered surface areas may be seen on heat treated rubies, especially around the girdle.

Usually the sintered areas are removed during the polishing process, but may be noticeable near facet junctions.

diffused color zoning


Much like in natural, untreated rubies, heat treated rubies will show straight, angular, or even hexagonal growth zoning.

However, untreated rubies will have more defined lines than the diffused lines in heat treated rubies.