This would add new items and blocks, but should not require a new world-gen since all of the base materials should be available in vanilla.
Concept:
Can create and transform base materials into other materials based on real life chemistry, using alchemical/chemistry practices.
Get some base material (dirt, rock, wood, ore, sand, whatever), separate out different parts of it through different methods (settling in water, burning, boiling, exposure to sunlight, dissolving, crystalizing…), then recombine them into different things.
This mod should have careful configuration options:
First, you should have an option to include spiritual or non-scientific (meaning unprovable and seemingly unlikely) beliefs. The influence of the planets on certain processes, for instance, or the ability to turn lead into gold.
Second, you should be able to turn on and off theoretical substances like the philosopher’s stone, alkahest, and the elixir of life, and choose whether or not they should have recipes, be findable in dungeons, etc.