This is optional, but placing sand inside of the shell to put out your smudge sticks will keep the shell clean, but a good wash will do just fine.
The abalone shell comes from a type of mollusk. They can be used a nice, decorative pieces around your home, but many cultures use them for spiritual purposes. Native Americans use abalone shells as bowls to burn sage, and they used feathers to waft the smoke away.
Abalone shells help balance the heart, crown and third eye chakra. are said to have properties for protection and balancing energies. Which is why it used when burning sage, palo santo or cone incense.
2"-3" shell - pink & white
3"-4" shell - tan & brown