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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.

Chaos Emeralds

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.

Sol Emeralds

These are the inter-dimensional counterpart of the Chaos Emeralds, guarded by Blaze. Eggman Nega often collects these for his own cruel intentions.

Master Emerald

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.