It is one thing to identify a ruby versus similar looking gems like spinel or garnets. To figure out if a ruby came from Africa or Burma is an entirely different story. This kind of detective work requires extensive training, a microscope, and prohibitively expensive lab equipment. Even with all these tools, lab gemologists are limited in conclusively identifying ruby sources.
There are two main methods used to determine the origin of a ruby, the same as with most other gems. One is Raman spectroscopy, which any professional lab uses. While the technical application and data processing is very complex, the short version is scientists send a laser through gem material (it has to be see-through for the laser), and the computer reads the light patterns that comes out of the gem. The computer then processes what elements are in the “unknown” gem material, and gives details about what concentrations the different chemicals are in the gem. This is how the lab gemologists determine chemical composition without damaging these precious stones.
Just the chemical composition of that gem is not enough to determine an origin. For that, the lab compares the information collected from that particular ruby to Burmese rubies, Siam rubies, Mozambique rubies, etc. In essence, they check their database for rubies with similar compositions. After comparing all these rubies they get an idea of where ruby is most likely from, but this is not always a guarantee of ruby origin.
Having this database is no small feat either. Each gem sample needs to be confirmed for not only their country of origin, but which specific mines they come from (when possible). This means assembling precise data for dozens, if not hundreds of other samples from all different sources globally. The more information in the database, the more accurate the result will be.
Rubies from different locations can have very similar chemistry. For example, rubies from Burma and Vietnam have been noted to be very similar in their chemical make-up. Because of this, scientists also check the inclusions, the other stuff mixed into rubies.
In these examples of silk there are very different formations. The silk in the Burmese ruby is finely woven in a very regular pattern. The African silk is much looser and disorganized overall. This is very common in rutile formations from these specific locations, but this can’t be used as a diagnostic. There are a large number of exceptions to this rule of thumb, like many other inclusions in rubies.
Some inclusions are region-specific and diagnostic, meaning the stuff that can’t be found in rubies from any other source. These are not always present in rubies, making the origin inconclusive, though the lab should have a good idea where the ruby comes from (as illustrated with the African ruby silk).
The one definitive distinction the spectroscopy gives in rubies is between naturally forming rubies and synthetically made ones. There are always trace amounts of various elements in natural rubies, since nature does not think about mixing whatever is in the ground together. These trace elements are absent in synthetic rubies, and many usually have chromium levels that far exceed their natural counterparts.
There are also a number of diagnostic inclusions in synthetics, though not all synthetic rubies show these features