Basic item obtained by smelting Sulfur Ore.
You can gain sulfur by smelting Sulfur Ore in a furnace, you will obtain on average 4-8 Sulfur per ore.
The actual specific details on what resources drop where and how are not yet fully understood.
What is known, all resource spawn rates are linked. Meaning that if you only gather metal ore and leave all other resources eventually there will be no metal ore spawning.