The Pearl of Power Amulet is a Uncommon Amulet found in Baldur's Gate 3.
There are no molluscs of power, alas.
Amulets are items that can provide a benefit of some sort when equipped. They can grant spells, abilities or even just be sold for a profit. Keep a few handy for those fights where the odds seem overwhelming, and you might be surprised at what you can achieve.
Where to Acquire the Pearl of Power Amulet
You can purchase this from Omeluum at Ebonlake Grotto once you have completed the "Help Omeluum Investigate the Parasite" quest.
Pearl of Power Amulet Effects
Pearlescent Restoration - You can replenish expended spell slots of your choice up to third level. Recharges on a Long rest.
To learn more about Amulets available in Baldur's Gate 3, check out the following article: