Blood Rock

Blood rock suffuses an area in which it is placed with the pure essence of war and violence. Sacred to war gods and priests of many evil gods, blood rock causes weapons to strike harder, claws to tear deeper, and blood to flow more freely. Five pounds of blood rock spread over a 1-foot area increases the lethality of any attack made by a creature standing in the area. Larger quantities of blood rock can affect larger areas. Double the threat range of all attacks made within an area affected by blood rock. A creature must be touching the ground in the blood-rock-enhanced area in order to gain this benefit. This increase in threat range does not stack with the increased threat range from the Improved Critical feat, the keen edge spell, or from the keen weapon quality. Simply carrying 5 pounds of blood rock around is not enough to gain the benefits of its presence. Blood rock must be placed in an area for a period of at least 48 hours before its presence is powerful enough to affect the area. Once placed, blood rock can be gathered up and placed in a new area. The new area still requires 48 hours for the effects of the blood rock to take hold.
Source: Dragon #313