Where do onyx gemstones drop

Thus far I have 2, 1 came from the end chest at the Raven Dungeon and I believe the other was completely some random drop, anyway the question is does anyone know where they drop consistently?

I also got one from a chest, but it was at Cold Vengeance/Frostmaw.

every end-dungeon chest has a chance of dropping them, that seems to be it so far. but it's all random, since those chests also drop diamonds, possibly the other gems, and golds/greens. there's no consistent source yet, but i suppose you could just find a really short dungeon and keep doing it, you'll get em eventually.

The chest at the end of the elite dungeon always drops an onyx. Every other chest drops an onyx about 10% of the time.

frost wurm is master but i didn't get one there ..
i have only one , for doing cyndir and the heart of mountains

I have done 4/5 parts of the elite "quest" and 1 in my party got a diamond while the other 2 of us got onyx. thx for the input and hopefully there will be a more consistent spot found for these tasty tid-bits that i crave!