Yea, as everyone has already said its all luck.
Last gem double odds I walked away with a perfect blood ruby, lunar, and two on my armor, one on helm and one on my magmatic. A few days later I perfected that magmatic totem and my mythic armor, and since then I have seen nothing and it's been a month or so and I try every night, so yea...dat luck. zzz
Still working on my helm and now I have a Kersh to worry about. Here's to double odds weekend again. xD