With the minimal information you provide, the coin is "possibly" a (1757) British, King George II silver Penny fairly small in size. The reverse of the coin may have "MAG BRI FR ET REX" around the outer edge, a large number "1" with a crown sitting on top of it, the date being divided by the crown. The "1" in the date might more resemble a "J" than a "1". If this sounds like your coin, it is not especially rare, but may fetch up to £65 GBP if it is in very good condition, or £5 GBP if it is in not such good condition. A reputable coin dealer will be able to give a more accurate valuation.
If the inscription in total reads GEORGIVS II REX on the obverse, with BRITANNIA on the reverse, your description lines up with a copper coin, but there were no copper coins minted in 1757 and all Pennies prior to 1797 were a small silver coin. You may have a privately minted coin or a medallion.
what is the georgivs vi rex imperator 1 d 1954 coin woth
A coin marked with "GEORGIUS" or "GEORGIVS" could be any British, British Colonial or British Empire/Commonwealth coin issued during the respective reigns of any of the six King Georges. George (I)(1714-1727) George II (1727-1760) George III (1760-1820) George IV (1820-1830) George V (1910-1936) George VI (1936-1952)
Look up coin dealers in your area and try one of them. A reputable coin dealer will confirm your coin as genuine and give you a valuation and maybe an offer to purchase it from you. Alternatively, try eBay.
I have a "Georgivs VI REX Imperator" coin with 3 bars on the back forming an open inverted triangle with a flower & stem in the middle. Wnat demonination is this coin and does it have any value?
"Georgivs Sextvs Rex" is Latin for "King George the Sixth". If the coin says only "Georgivs Sextvs Rex" on the obverse, it is likely not from Britain but rather one of its colonial holdings - the name of the colony would be on the coin somewhere. Any bank in this colony might then be interested in buying it, especially South Africa.
Britannia can be found on the reverse of a Britishnon-commemorative 50 pence piece. Britannia also appeared on predecimal Pennies and pre-1936 Halfpennies.
The words Georgivs II Rex on a coin (or similar) would translate as George the 2nd King, or King George the 2nd if you prefer.
Howmuch
No, it is not a very rare coin (as it is believed that 1,698. 000 of them were out in 1952). You can sell this with about $9 if the coin is in good state and with about $16 if the coin has never circulated.
The only George III coins with Britannia on the reverse are the Twopence, Penny, Halfpenny and the Farthing, but none of them had a milled edge. From 1797, the Penny was 36mm in diameter, the Twopence was 41mm in diameter and both coins were made from copper.
Other than for commemorative 50 Pence coins, Britannia has been on the reverse of the 50 Pence coin since it was first issued in 1969 until 2008 when the new design British coins were issued.