Including abalone shells in your smudging rituals means you are incorporating all four of the earth’s elements: the shell represents water, the smoke represents air, the unlit herbs or sticks represent earth and once they’re lit they represent fire.  I like to follow the 5 elements of Chinese medicine, which uses a 5th element, metal. Abalone shells are naturally grey and silver which happens to be the color and representation of metal. 
How to conduct a smudging ritual with abalone shells
Firstly, you’ll need smudging sticks or herbs, and an abalone shell.  Palo Santo smudging sticks or a  variety of herbs you might use for smudging all have different energies, for example, lavender promotes calming, white sage releases and clears energy, and mugwort is said to stimulate dreams.
You may wish to use a layer of sand inside the abalone shell to protect the natural shine that it has, from any smoke or embers.
Using a match, light your herbs or Palo Santo smudging sticks
Rest the sticks or herbs in the abalone shell, using it to collect any ashes or embers as the sticks or herbs burn
To cleanse a person or object, use a feather to brush the smoke around them
You may wish to walk around a space with the sticks or herbs, allowing the smoke to waft into the corners and ceilings
Abalone shells have holes in them, so ensure any hot embers don’t fall through onto flammable materials such as carpet or bed linens
If the smudging sticks have been resting in the abalone shell for awhile, the shell may get hot, so use caution when handling it. 
So, there you go! Smudging is a great practice to use when your home or work space needs clearing of negative energy.