CCTV footage shows the thief entering the Adelaide Street store on 1 February, asking to inspect a range of precious stones.
When a staff member was distracted, the man reportedly pocketed a diamond valued at $30,000 and then ran away.
Police have released images of the robber who was wearing a grey felt hat, green button-up long sleeve shirt and grey suit at the time of the event.
The man has been described as Caucasian with a muscular build and about 185 cm tall. He has sandy-coloured hair and blue eyes.
The incident adds to a growing list of high-priced robberies that occurred in February. As previously reported by Jeweller, police are still hunting for a man suspected of targeting jewellery stores in Queensland, NSW and Victoria as well as a group of thieves who pulled off a $50 million diamond heist at Brussels airport.
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