Assuming you mean a British George III Crown, it depends on the date and condition. Many of these coins are found with at least moderate amounts of wear and those in mint state or about uncirculated condition can fetch a premium, even for common dates.
1820 coins are worth the least, little more than bullion (about $25 or so at the time of writing) in worn condition or about $45 if in decent condition. Of course an uncirculated specimen can be worth several hundred dollars.
1818 and 1819 are worth moderately more, about $50 or so if in decent condition, although still little more than bullion if very worn.
However, the 1819 has a variety where there is no stops on the edge of the coin, this is worth about $55 or more depending on condition.
Being a short series, this is a pretty easy set to obtain a date run (only crowns dated 1818, 1819 and 1820 were produced for George III crowns, ignoring of course the Bank of England tokens and the "dollar" issues)
The value of a 1939 George VI British silver half crown can vary depending on its condition and wear, but ranges between $3 and $20.
There were no 1740 British Crown coins minted. The Crown coin was not regularly minted during the reign of King George II.
The value of a George VI half crown coin will depend upon its condition and how much the seller wants for it. You can expect to pay anything in the region of $1-$30 for this coin at auction.
Between $25 and $318. In the future please add a condition of the coin so I can value it more precisely for you.
There was no 1946 British Crown minted.
Modified coins have no value as a collectible. Any value would be associated with the necklace.
Between $16 and $60. In the future please add a condition of the coin so I can value it more precisely for you.
George Washington George Washington
The king value of the diamond in the royal crown is immeasurable due to its rarity and significance.
The 1950 Half Crown of Georgius VI is not made of silver, but of cupro-nickel. 50% silver Hlaf Crowns were issued until 1946. Source: Wikipedia
I have a vase with a crown on the bottom
There was no British Crown minted from 1938 to 1950 inclusive.