Blast Furnaces turn Coal Blocks into Diamonds and Sandstone into Quartz

In real life, extreme heat and pressure turns coal into diamonds (carbon) and sandstone into quartzite (silicon dioxide).

In Minecraft, having more paths for progression of tools/armor and building/redstone would only make the game more accessible to different types of players.

I don't think this would be too overpowered, as requiring specifically the Blast Furnace means the player still needs to at least have iron.