Factorio Forums

1. High-quality stone was placed in a furnace
2. High-quality stone cannot be smelted into stone brick in a furnace, because the furnace cannot set quality for the smelting recipe. 3. The furnace should have automatically matched quality of recipe to quality of input, the same way that furnaces automatically match recipe to input ore type.
4. This happens always for raw stone with higher than normal quality. Did not test if this extends to other ore types.

You need 2 stone to smelt it into 1 stone brick.