natural sapphire inclusions

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

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

untreated sapphires

mineral crystal

Unaltered mineral crystal inclusion in an untreated, natural sapphire
Photo courtesy of Scott Papper, GIA GG, AJP, CM (NAJA), Global Gemology & Appraisals

​Unaltered mineral crystal inclusions such as hematine, zircon, spinel, calcite and mica, to name a few.

straight / angular growth

Sharp, angular growth in a natural sapphire
Photo courtesy of Scott Papper, GIA GG, AJP, CM (NAJA), Global Gemology & Appraisals

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

silk


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

fingerprint


​Networks of tiny, liquid-filled tubes that look like a fingerprint.

heat treated sapphires

discoid fracture

Discoid fracture in a heat treated sapphire
Photo courtesy of GGTL Laboratories

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

partially healed fingerprint

Several fingerprint inclusions inside a natural sapphire
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 sapphires, 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 sapphires, heat treated sapphires will show straight, angular, or even hexagonal growth zoning.

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