Hard to Find Minerals.

[SeniLiX]

Found Bauxite and Ruby in Wasteland Biome.

 

[zanesin666]

So atleast I can add wasteland to my useful biome list.

So for Bauxite it'll spawn in PLAINS, FOREST, and WASTELAND for sure.
Ruby I have definetly found in Rainforest, Forest.
Emerald and Sapphire I have found in FOREST biomes.
I have found lots of diamonds in Rainforest Biomes.
I've only seen Saltpater or whatever it is in Desert Biomes.

 

[SilvasRuin]

Diamonds aren't biome specific, they are just very luck based.

 

[Antice]

I think saltpeter only spawns in deserts biomes indeed. I have a tough time finding any kind of desert in my current world, so i cannot confirm if XL biomes work.
Sulfur is a nether only ore tho. altho you have a chance at getting some from vanilla netherrack also if you use the pulverizer... 10% chance if i remember correctly. but who in their right mind would spend power on turning netherrack into cobble???