Hi again, Bronwyn and all,
The site I was thinking of is <www.geminterest.com>. It is in French, but you should be able to make out what you need to with the help of our good friend Google Translate, which is right most of the time. There is a box on the left near the top on the home page which shows that there are 1491 pictures of gem inclusions. If you click on this inclusions link it brings up the inclusions page and the list of gems. If you click on a gem, you get photos of inclusions for that gem. There are many photos of inclusions in Ramaura, Kashan, etc., rubies and I expect also for natural. This would be a good place to start and maybe you can distinguish your feather.
Another piece of advice I got over on gemology on line was:
“With immersion, natural mineral inclusions will go light to dark as you rotate the stone. Solid inclusions typically found in synthetics will remain dark in all directions.” Perhaps this will help. Immersion is helpful, whereas darkfield, so useful for diamonds, can be confusing with colored stones. I don’t remember hearing this in my gemology training. Maybe I missed it.
You might find other useful info on the gemology on line forum, where a lot of the big gemologists hang out, including my hero, Bill Hanneman.
Again, good luck! You need to buy me a beer if it turns out to be natural! If it’s synthetic I’ll buy the beer and watch you cry in it!
royjohn