Magyar Királyság was Hungary's name used in 1840. The country was under Austrian control until 1918. Franz Joseph (Ferencz Jozsef) was king of Austria. So it all ties together, Helissente. You have a 10 korona gold coin from Hungary, just as you report on our questionnaire. There are 20 and 100 korona coins minted with the same pattern.
Here are the stats for these koronas:
10 KORONA: 18 mm diameter, 0.098 troy ounces gold
20 KORONA: 24 mm diameter, 0.196 troy ounces gold
100 KORONA: 35 mm diameter, 0.980 troy ounces gold
You can find the base value of your coin, often called the melt value, by multiplying the ounces of gold by the current price of gold. Using the web site kitco.com, the current price of gold is $1186 US dollars per troy ounce. Check that price now, because it changes every day. Remember that when speaking of precious metal, 'troy ounce' is the same as 'ounce' -- the 'troy' is understood. The melt of these coins is, at the moment:
10 KORONA: 0.098 x 1186 = $116 US dollars
20 KORONA: 0.196 x 1186 = $232 US dollars
100 KORONA: 0.980 x 1186 = $1162
Tomorrow the value of gold will be different. Look it up.
Since your coin has been used a jewelry, Helissente, collectors will not pay a premium over melt value to add your coin to their collection. That means your coin is worth melt value. A dealer would probably pay about $50 less than melt so he or she could sell it at melt, keeping the mark-up for maintaining the dealership.
Normal, non-jewelry coins carry a 'collector premium' added to the melt value to determine value, as follows:
circulated: add $30 to the basic melt value
uncirculated: add $75
circulated: add $50 to the basic melt value
uncirculated: add $100
circulated: add $500 to the basic melt value
uncirculated: add $2000
restrike: add $0
There are a few *better date* 10 and 20 korona coins where the premium way goes up over the premiums listed above, as follows:
1895: add $2000 to the basic melt value
1915: add $3000
1910, 1913, 1915, 1916: add $200 to the basic melt value
If you have a better date, or if your calculations produce a value exceeding $1000, be sure to check with a knowledgeable collector or coin dealer. An in-person appraisal is always needed for such coins. Remember, also, that valuable coins are widely counterfeited today, so be sure to deal only with people you trust.