One of these small, black spheres might be mistaken for some common bead, a marble, or perhaps an unusually black but lusterless pearl. 

Each is about three-quarters of an inch in diameter and quite heavy, weighing almost an ounce. 

One can be hurled up to 3" distance. Upon impact, the bead will send forth a burst of force which will inflict 5-20 (5d4) hit points of damage upon all creatures within a 10-foot radius of its center. Each victim is allowed a saving throw vs. spell. Those who save will be thrown out of the blast area, but those who fail to save will be encapsulated by a sphere of force after taking damage. 

The sphere will form around any and all such creatures in the 10-foot radius area, even those of large size, and will persist for 3-12 rounds. 

Victims will be unable to escape except by the same means used to bring down a wall of force spell. 

From 5-8 of these beads are usually found at one time.