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Iridescent fingerprint in a ruby from the Thai/Cambodian border.
Rose channels in Thai/Cambodian ruby. These are often confused with rutile silk in corundum, but they are easily distinguished as they run in entirely different crystallographic directions. Rutile silk unmixes in three intersecting directions (60/120°) parallel to the faces of the hexagonal prism in the plane of the basal pinacoid (90° to the c-axis). In contrast, Rose channels form parallel to the edges of the rhombohedron, in three directions, but only two in the same place, oblique to the c-axis. They intersect at 86.1/93.9°.
A chalky angular pattern, viewed here in shortwave UV illumination, is a strong sign of heat treatment. Many rubies from Mong Hsu, Myanmar, are heated to remove the blue zones that are often present in the natural material.
Cottony heated diaspore silk in a ruby from Jegdalek, Afghanistan.
When iron-poor rubies from metamorphic deposits are heat treated, they often develop angular chalky zones when viewed in shortwave ultraviolet light. A great example of this is shown in this photograph, taken with Magilabs Deep Ultraviolet tool.
Spall marks on a natural on the girdle of this Thai/Cambodian ruby reveal the heated nature of this stone.
Thai/Cambodian rubies like this often show thin film inclusions that light up under fiber optic illumination.
Melted crystals are surrounded by runny channels in the heat-altered fingerprints in this Thai/Cambodian ruby.
This small melted crystal surrounded by an iridescent heat-altered fingerprint is a typical inclusion in Thai/Cambodian ruby.
Virtually all Mozambique rubies contain exsolved rutile silk. These needles consist of two connected crystals, one a titanium-rich portion of high relief (rutile) and at the broad end, a Ti-Fe “daughter” crystal (probably ilmenite) of lower relief. When such a gem is heated, the daughter portion may start to break down, resulting in a mottled appearance on the daughter platelets.
The mottled appearance of the platelets suggests this Mozambique ruby was heated.
Thin films such as these are a distinctive feature of Thai/Cambodian ruby.
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