With the latest update, players have the ability to smelt and growing, among other random fixes. Changelog below.
Minor release 3.2 (Furnaces – No more unlimited items)
- Furnaces! Every available block and item can now be gathered, crafted or smelted into.
- Grow trees! Saplings dropped when harvesting leaf with Shears.
- More tiles such as thin glass, and half blocks in different material.
- Gold, diamond and iron ore can now be gathered (smelt them for stronger tools)!
- Fixes: less flickering/Z-fighting on some devices, mobs have correct health, fixed rendering of fence gates and half blocks in hand.
Note of warning to those updating though, the game may crash when tapping on an empty furnace inventory slot. The developers seem to be aware of this, so I would expect an update addressing this shortly.