The Secret Stones (TotK) are introduced in Tears of the Kingdom as godlike Zonai artifacts. Those bestowed with a Secret Stone are often known as Sages. They are tear-shaped gems with the ability to amplify their users' inherent powers. Otherwise, these artifacts have no known powers of their own. When possessed by individuals with special powers, the Secret Stones gain an attribute and a corresponding Zonai inscription. The stones are commonly worn in place of jewellery.

Known wielders of Secret Stones:

Secret_Stone_of_Light — Rauru, on his right hand
Secret_Stone_of_Time — Sonia, Zelda, on their necks via a necklace
Secret_Stone_of_Wind — The Sage of Wind of the Rito, including Tulin, on their ankles via an anklet
Secret_Stone_of_Fire — The Sage of Fire of the Goron, including Yunobo, on their waist via a waistband
Secret_Stone_of_Water — The Sage of Water of the Zora, including Sidon, on their hands
Secret_Stone_of_Lightning — The Sage of Lightning of the Gerudo, including Riju, hanging from their ears via an earring
Secret_Stone_of_Spirit — The Sage of Spirit, Mineru, on her neck via a neckpiece
Secret_Stone_of_Darkness — The Demon King, Ganondorf, on his forehead

The below entry is a popular depiction, but non-canon.
Secret_Stone_of_Gloom — Midna