Lockets were created by Max Hamilton and were given to the three original mermaids in the 1950s. They were created as an attempt to make them embrace their abilities. Initially, all of them had a photo of the mermaids inside.
Cleo's locket originally belonged to fifteen-year-old Gracie Watsford, Charlotte's maternal grandmother, in the 1950's.
Emma Gilbert found the locket at the bottom of the Moon Pool in "Party Girls". After Miriam Kent almost stole it, she gave it to Cleo for safer keeping." In the two-part episode "The Gracie Code," Max tells Lewis McCartney that he made the locket for Gracie, the love of his life. After being reminded that she could never be human again, Gracie threw it into the moon pool where Emma found it 50 years later. Cleo's locket has a blue stone - presumably a sapphire; blue for the ability to control water. She stopped wearing her locket sometime during season three.
Emma's Locket originally belonged to fifteen-year-old Louise Chatham in the 1950's.
Louise gave her locket to Emma, as she believes that all of them should be together. Emma's locket has a white stone - presumably a diamond; white for the ability to freeze water. Cleo is seen wearing white stoned locket after Emma has gone to the vacation. While Emma was on vacation, Cleo was wearing her locket, until she got her crystal necklace.
Rikki's locket originally belonged to fifteen-year-old Julia in the 1950's.
While on a date with Zane Bennett, Rikki spotted the locket on the showcase of a jewelry shop, from deceased estate. Zane then asked Miriam (Zane's ex-girlfriend) if girls liked getting jewelry and Miriam spitefully bought the locket, so that she could make Rikki jealous.
Rikki tried to get the locket back, but lost. Zane then made a deal with Miriam that if he kissed her, she would part with the locket; Miriam then threw it into the harbor. Emma and Zane both jumped into the water to get the locket, with Emma nearly being exposed. Emma hid behind a post and let Zane search for it instead, and he found it after two tries. Louise Chatham said that Rikki deserves it because she kept the secret from Zane. Rikki's locket has a red stone - presumably a ruby; red for the ability to heat water.
In Mako: Island of Secrets, Rikki does not wear hers, showing that she has lost contact with Emma as well.