...Clark accepted the offer on the condition that the brick and the miner return with him to Chicago, and took the brick to a blacksmith for analysis.
The blacksmith cut off a corner of the brick and determined that the brick was pure gold.
On the trip to Chicago, the miner vanished and further analysis of the brick found that the sides and corners were indeed gold but the main body of the brick was worthless.
Think about it.
This act was copied and soon the phrase "to sell someone a gold brick" came to describe a swindle and to "gold brick" someone came to mean defrauding them."