The new 50p coin will be available from March 29 next year, the day Britain exits the EU at 11pm.
Mr Hammond has issued an order to the Royal Mint to draw up a design for the coin, which will be signed off later this year.
It is not know whether the coin will be a collectors edition or released into circulation for coin collectors to find in their spare change.
Millions of Brits collect coins and often rare ones can sell for hundreds and sometimes thousands of pounds.
The rarest 50p coin in circulation is currently the Kew Gardens 50p which sells for £175,000 on eBay.
What are the most valuable 50p coins?
HAVE a rummage through the change in your pocket for rare 50p coins because they could be worth a small fortune.
Kew Gardens, up to £160
This rare commemorative coin was created in 2009 to celebrate the 250th anniversary of London’s Kew Gardens. Only 210,000 of these coins were issued and a quick check online shows up that a circulated coin with this design sold for after it got 25 bids.
Sir Isaac Newton, up to £77
At first, just 375 of the Sir Isaac Newton coins were released into the tills at Woolsthorpe Manor in Lincolnshire, the birthplace and home of the famous scientist, but more of the coins were slowly released into circulation - adding up to a total of 1.8million. The majority of these coins are still boxed in protective packaging and they're selling for around .
Jemima Puddle Duck, up to £13.50
There are only 2.1million of these coins in circulation and one of the coins recently sold for 27 times its value at .
Suffragettes, up to £7.50
There are currently 3.1million of the coins in circulation. Recently, one coin that had been in circulation fetched - that's 15 times its face value.
WWF, up to £4.50
There are 3.4million coins in circulation and they are hugely popular amongst collectors. We found one that was recently .
Britannia, up to £1.81
Britannia replaced by the new Royal Shield in 2008 as the standard 50p design, and none have been issued since, making the ones minted in that year valuable to collectors. Only 3.5million were issued into circulation and one recently sold on .
Around 210,000 coins of this design were minted in 2009.
The rarer the coin the most sought after and valuable it becomes.
A spokesman for coin collecting website Change Checker said the new Brexit coin could potentially become very valuable - though they couldn't put a value on it yet.
They said: "As this is such a landmark event in British history, the Brexit 50p coin could potentially become very sought after, however there is also the possibility that due to the controversy of Brexit some people may decide to boycott the coin entirely.
"It seems that there is currently a demand for a Brexit coin to be released, as commemorative souvenirs and medals can already be found for sale on eBay.
"Whilst we wouldn’t be able to put a value on the coin, the previous commemorative 50p coins released in 1973 and 1998 to mark Britain’s entry to the EEC are very popular amongst collectors."
Coins with defects or errors can also be valuable to collectors too.
The Sun has been told that the "friendship with all nations" phrase instead of any symbol is the firm preference of ministers for its reverse side.
The Royal Mail – which is no longer under the Government’s control - has repeatedly refused to issue a commemorative Brexit stamp, insisting the event is still too politically controversial.
A 50p coin was issued to mark Britain’s entry into the European Economic Community in 1973, as well as our 25th anniversary of joining in 1998.
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