After prospecting almost 8K stacks of elementium ore its pretty obvious Ocean Sapphire and Zephyrite have the highest drop rates and that Inferno Ruby is the lowest drop rate.
Every time I prospect I clear my bags, and Ocean Sapphire and Zephyrite are always at the top of the list.
Seems like drop rate is:
Ocean Sapphire=Ember Topaz>Dream Emerald=Amberjewel=Demonseye>Inferno Ruby
Zephyrite>Jasper=Alicite=Hessonite=Nightstone>Carnelian
I am speaking from pure experience here this is not what it "feels" like, this is what it is. While I have not recorded my results, I have always noted which dropped most and which dropped least and its always Blues are the most and Reds are the least.