Micro-World Gems & Gemology, Fall 2021, Vol. 57, No. 3

Apatite in Blue Sapphire

An iridescent apatite crystal seen in an untreated star sapphire.
An apatite crystal is suspended over a cloud of rutile silk in this untreated star sapphire. Photomicrograph by E. Billie Hughes; field of view 6 mm.

One of the beauties of working with gemstones is that each time you peer into a stone, you get a glimpse of the universe held within. When we first examined the scene in a star sapphire (see above), we were delighted with the view. A feature that immediately stands out is the triangular crystal, which displays terraced growth features and iridescence on the surface when illuminated with a fiber-optic light. Analysis with micro Raman revealed that this crystal is apatite.

What makes the scene even more stunning is the way the crystal seems to float over a cloud of rutile silk. This same silk is what creates asterism in the stone.

While in this case the apatite crystal resides in a sapphire from Sri Lanka, apatite has also been reported in corundum from a variety of sources, including Afghanistan, Cambodia, Madagascar, Myanmar, Nigeria, Pakistan, Tanzania, Thailand, the United States, and Vietnam.

Apatite can be found not only in ruby and sapphire from different origins, but also in many other types of gems. In our laboratory, we have encountered apatite inclusions in emerald, spinel, and garnet.

Apatite is a relatively common mineral, so it is not surprising to find it so often as an inclusion. Although it may occur frequently, in this instance it is anything but mundane.

E. Billie Hughes is a gemologist and co-founder of Lotus Gemology in Bangkok.