The only British 22 carat gold coins issued in 1899 were the Sovereign and the Half-Sovereign. The Florin was a silver coin from its introduction into the currency in 1848.
Please check your coin. The word "spade" referring to British coins is a reference to the "spade" shaped shield on the reverse of gold Guinea and Half-Guinea coins minted between 1787 and 1800. The Florin coin was not (re)introduced into the British currency until 1848.
The Florin (Two Shillings) was not introduced into the British currency until 1848. A much earlier gold coin called the Florin and Double-Florin (or Double Leopard) was introduced around 1344 for trade with with Europe, but due to issues with the value of gold, the coin was withdrawn soon after its issue. France and Italy both had similarly named coins on which the English coin was based.
The Australian Florin was never minted in gold.
A gold florin typically weighs around 3.5 grams.
The Australian 1954 Florin (Two Shillings)(Royal Visit Commemorative), was minted only as a 50% silver coin. There is no evidence suggesting that the coin was ever produced in gold. If you have a gold coin, it is because somebody had it plated. Modified coins have no value.
Depending on which of the Commonwealth countries it came from, a 1964 Florin (Two Shillings) would be made from either a copper-nickel alloy or a 50% silver alloy, not gold. Somebody may have gold plated it. Modified coins have no collector value.
A $5 gold coin that was minted in 1899 - aka - Coronet Head Half Eagle - is worth in fine condition (F12): $250; its value increases to $400 if it is in a mint state of MS60.
The florin was used in Italy during the Renaissance. It was equal to 72 grains of gold. It was called the Florentine florin. (Florence, Italy) __ The British Florin was introduced into the currency in 1848 with a value of Two Shillings. The coin remained in use until decimalisation in 1971 when it was replaced by the 10 New Pence coin. The collector value of a Florin would depend on the year and condition of the coin.
Florin
Assuming the coin is circulated and has no "S" mintmark, retail value is $490.00-$560.00 depending on the actual grade of the coin. 1899 Liberty Head Half Eagles are a high mintage, very common date gold coin. NOTE: If the coin has been used as a jewelry piece, or cleaned, value is for the gold content only.
In the 1500s, an Italian florin was worth about 3.5-3.6 grams of gold. The exact value fluctuated depending on the purity and weight of the coin, but it was generally accepted as a stable and reliable currency in Europe.
The collector value of a coin is lost when the coin is modified. Any value would be associated with the brooch.