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Emerald did not originate from fanon, and more information can be found on their respective wiki(s). You may read more about it on the following wiki(s):
Emeralds are a type of precious gemstone. In the Sonic series, there are three main types; Chaos Emeralds, Sol Emeralds and the Master Emerald, with a couple of other obscure types.
Main article: Chaos Emerald
Chaos Emeralds are powerful gems in the
Sonic series; there are six of them, with a seventh, the grey emerald, acting as a stabiliser. Dr. Eggman likes to collect these as they give him power, and it is usually Sonic's job to pick up the pieces.
In Sonic Heroes 2, the locations of the Emeralds are Aqua Lake Zone, Great Turquoise Zone, Sandopolis, Casinopolis, Scrap Brain Zone, Station Square and Sleeping Egg Zone.
These are the inter-dimensional counterpart of the Chaos Emeralds, guarded by
Blaze. Eggman Nega often collects these for his own cruel intentions.
Main article: Master Emerald
Is the supervisor of the Chaos Emeralds. In most, indeed all canonical, games it is guarded closely by
Knuckles the Echidna; in Sonic Heroes 2 it is guarded by Knuckles and Shade the Echidna.