Cascarilla, Eggshell, Santeria
Cascarilla is powdered eggshell. The shells are so finely ground that it feels as soft as baby powder. 
Any Botanica or store that caters to New Age and Magick rituals will have Cascarilla. 
 When removed from the cup, it maintains its form and can be used as one would use a soft piece of chalk. 
Or, if mixed with water, you will find that the soft chalk dissolves easily. 
If you choose to buy the Cascarilla, you will normally see it packed into what I call a “ketchup cup.” 
For most purposes, it is used as a piece of chalk, so the shells sold in stores are convenient.
Cascarilla repels negative energy and the vibration of negative energy.