a rock you decided was magic, and somehow it works on your brain
means A small object—charm, stone, or trinket—believed to carry magical power that protects its owner or brings good luck.
from From French talisman, drawn from Arabic ṭilsam, a charm or magical figure, which itself borrowed from the Greek telesma, meaning a religious rite or consecration—from telein, 'to complete' or 'to perform a ritual.' So the word's long journey runs from a Greek ceremony, through Arabic enchantment, into European pockets, slowly transforming from 'a thing made holy by ritual' into 'a thing you carry for luck.'
hope diamond — 45.52-carat blue diamond at smithsonian, allegedly cursed, owned by kings and socialites since 1600s
elephant's foot in uganda — dried foot of a tusked elephant kept as protective charm in kasubi tombs, kampala
the kohinoor — 105.6-carat diamond in british crown jewels, believed to bring luck to female owners only