I don't think there IS oil shale anymore. At least it's not listed in biome ores on Rh discord.
"JaxTeller718 - Yesterday at 8:12 PM
Ores have changed in Ravenhearst. Below is a list of what ore you can get from where.
Snow = Potassium
Burnt = Coal and Fertilizer
Desert = Oil
Forests = Iron
Plains = Lead
Wastelands = Copper, Zinc and more chances of finding Diamonds
Coal, Potassium, Rock Salt, Limestone and Carbon can be mined from breaking underground rocks with a Pickaxe. Keep in mind the better your Pickaxe the better your chances of find these minerals. So an Iron pickaxe is better at harvesting them than a Stone Pickaxe."