Every coin has two sides to it, now look out for the one that comes in two parts.

A small percentage of the Rs 10 coins released in the city this week have a “defect” that might cause the centre of the bi-metallic piece to be detached from the outer ring with use.

The coins, comprising a cupro-nickel centrepiece and an aluminium-bronze rim, are the first of their kind to be minted in the country and were originally scheduled to be released three years ago. “We had to delay the release of the coins because of the defect,” a senior RBI official said on Friday.

The problem was first detected by personnel operating counting machines at the Noida mint where the coins were manufactured. “While counting they found that the centrepiece could be separated from the rim in two to three coins out of every hundred,” the official said.

The defective coins have been withheld but officials suspect that the same problem might occur in two to three per cent of the remaining bi-metallic pieces after some wear and tear.

What it means is that the 10,000 bags of bi-metallic currency — 2,000 coins per bag — received by the Calcutta branch of the RBI could contain four to six lakh defective coins.

Collectors may not complain if someone gives them such a coin — stamps with errors are counted among the rarest and most valuable — but others might.

For those stumped by the toss of the two-piece coin, there is a way out to make their money count. “Both pieces of the coin must be taken to the RBI branch for exchange. Depending on their condition, the bearer will be reimbursed,” a senior official promised.

Another official said the RBI could not have rejected the coins after minting them because of the huge expenditure involved in the process. “If the coins are dumped, the loss would amount to several hundred crores of rupees.”

The RBI is releasing about 30 per cent of the coins over the counter and 70 per cent through banks.

Rabi, an unauthorised broker selling currency near the General Post Office, said: “The Rs 10 coins are selling like hot cakes. I sold 15 pieces for Rs 100 each and five for Rs 150 each on Tuesday. The buyers were mostly coin collectors.”

RBI spokesperson Alpana Killawala declined comment on the “technical problem”.