From Wikipedia, "Land Mines":
"The Ming Dynasty (1368-1644) text of the Wubei Zhi (Treatise on Armament Technology), written by Mao Yuanyi in 1628, outlined the use of land mines that were triggered by the heat of a slow-burning incandescent material in an underground bowl placed directly above the train of fuses leading to the mines buried 3 ft beneath.
The booby trap of this mine system had a mound where weapons of halberds, pikes, and lances were dug in, meant to entice the enemy to walk up the small mound and claim their stolen prize of war booty. When the weapons were removed from the mound, this movement disturbed the bowl beneath them where the butt ends of the staffs were, which in turn ignited the fuses.
According to the Wubei Huolongjing volume of the 17th century, the formula for this slow-burning incandescent material allowed it to burn continuously for 20 to 30 days without going out.
This formula included 1 lb of white sandal wood powder, 3 oz of iron rust (ferric oxide), 5 oz of 'white' charcoal powder (from quicklime), 2 oz of willow charcoal powder, 6 oz of dried, ground, and powdered red dates, and 3 oz of bran."
Incidentally, the sandalwood makes this quite expensive.