Obsidian is the ultimate cleaner. It pulls anything "bad" out of stones, people (you and others), and your environment. It shields against negativity.  Since these are smaller pieces, they will need to be cleaned more frequently.  They would be great in a grid or on an altar.
 
Size:  approximately 1" x 1" x .25".
 
Price is per star.  
 
Available:  1 and 2.