Heated Sapphire Inclusions

First Published: 7 September 2026

Heated Sapphire Inclusions

Explore inclusions in heat-treated sapphire in Hyperion, the Lotus Gemology inclusion database. Hyperion contains photomicrographs of inclusions and internal features in natural sapphires that have been subjected to heat treatment, documented with information on geographic origin, lighting conditions, field of view, photographer and published references.

When Sri Lankan yellow sapphires with exsolved particles are heat treated, magnesium exits the particles and creates yellow-producing trapped-hole color centers. The result is color concentration around the particles, a process termed “internal diffusion” by gemologist, John Koivula.
When Sri Lankan yellow sapphires with exsolved particles are heat treated, magnesium exits the particles and creates yellow-producing trapped-hole color centers. The result is color concentration around the particles, a process termed “internal diffusion” by gemologist, John Koivula.
Low iron rubies (and pink and padparadscha sapphires) from localities like Mogok, Mong Hsu (Myanmar) and Sri Lanka will often display chalky zones in short wave ultraviolet after heat treatment. Here we see an excellent example in a heat-treated padparadscha sapphire from Sri Lanka. This fluorescence is positive proof of heat treatment.
Crossing twin planes in a sapphire from a basaltic source. These are secondary glide twins, created by pressure after the stone grew, and form parallel to the rhombohedron faces, intersecting at 86.1 and 93.9°.
Certain type of solid inclusions are heat sensitive and may alter when the gem is heat treated. Here we see crystals that have altered into “snowball” like forms. In addition, the coefficient of thermal expansion of the included crystals was greater than corundum. Thus when heated, they expanded more than the surrounding sapphire, producing glassy discoid fissures.
When a rutile-silk containing sapphire (such as this stone from Nigeria) is heated, the titanium from the rutile moves into solid solution in the sapphire, coloring the area around the rutile blue, creating a distinctive “ink spot” internal diffusion pattern.
When low-iron sapphires are heat treated, a chalky shortwave fluorescence often develops. This generally is related to colorless or lightly colored regions of the gem, and so follows the crystallographic structure, as is seen here. This is strong evidence of heat treatment.
When a rutile-silk containing sapphire (such as this stone from Sri Lanka) is heated, the titanium from the rutile moves into solid solution in the sapphire, coloring the area around the rutile blue, creating a distinctive “ink spot” internal diffusion pattern.
When a rutile-silk containing sapphire (such as this stone from Sri Lanka) is heated, the titanium from the rutile moves into solid solution in the sapphire, coloring the area around the rutile blue, creating a distinctive “ink spot” internal diffusion pattern.
Fingerprints are made up of tiny negative crystals. This often contain carbon dioxide and were formed at depth under high pressure. When the gem reaches the surface, the pressure pushing out can be quite large. Thus they are particularly heat sensitive and often burst if the gem is heat treated. Here we can see what happens when such a fingerprint is subjected to heat treatment. Each tiny negative crystal bursts, creating a series of microfractures.
A small crystal with streams of particles coming off it in a heated Madagascar sapphire. Particle streams such as this form because an inclusion creates a barrier to growth behind it, resulting in the trapping of tiny fluid inclusions.
Many crystals contain shallow fissures on their surfaces. In sapphires from Sri Lanka, Myanmar and Madagascar, these fissures often contain yellow stains. High-temperature heating not only destroys the yellow stains, but begins a process of healing, where the fissures turn white and start forming fingerprints, as we can see here.

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Heat treatment can alter inclusions and other internal features in sapphire. Changes may include modification or dissolution of rutile silk, alteration of mineral crystals, decrepitation of fluid inclusions, changes to healed fissures and the formation of heat-related features. Such evidence can be important in determining whether a sapphire has been heated.

Heated Sapphire Inclusion Photomicrographs

The Hyperion heated sapphire gallery includes microscopic features documented in heat-treated natural sapphires. Each entry is accompanied by descriptive information and, where available, references to the gemological literature.

What Inclusions Can Reveal About Heat Treatment

Microscopic examination is an important part of detecting heat treatment in sapphire. The condition of mineral inclusions, rutile silk, fissures and other internal features can provide evidence of exposure to elevated temperatures. These features are evaluated together with other gemological observations when determining treatment status.

Hyperion combines inclusion photomicrography with supporting gemological information so that heat-related features can be compared with documented examples in treated sapphires.

About Hyperion

Hyperion is the Lotus Gemology searchable inclusion database. It allows users to browse gemstone inclusions by gem type, geographic origin, treatment and keyword.