I think it's some kind of arabic!
True.
The British 20 Pence coin is seven sided, or heptagonal, to help with identification and to avoid confusion with other similar sized coins.
You need to give more information. What color was the coin after the reaction, and did the silver nitrate solution change color?
Just looking at the coin carefully will help. The name of the country might not be in English. For example, a French coin will say Republique Francaise on it, and a Swiss coin will say Confederatio Helvetica. A good coin book will help find the answer.
Go to a coin dealer or a jeweler, they have tests that will verify if the coin is gold or not.
The 11-sided design was chosen to help make the coin easy to tell apart from other coins, especially to help people who are visually impaired or blind. Those of us who are sighted can tell by its color, but for someone who relies on touch the 11 sides distinguish it from similar sized pieces such as quarters and halves.
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Coins are certified by NGC and PCGS. A coin shop can help you or search on the internet. It costs something to get a coin certified.
If you have lost a coin collection, we will probably not be of much help. If you are looking to buy one, you could advertise on eBay or visit a local coin dealer.
Silver, not gold. E Pluribus Unum, not "eplurius" (check the spelling on the coin) Plus, ALL coins have that motto so it doesn't help to ID a particular item. Presumably it IS a dollar coin, at least. In that case the gold color is because it was plated for use in jewelry or similar. That would make it an altered coin worth only its metal value, about $14 as of 08/2008
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