Use a magnet to check them. if it doesn't catch it may be silver. Aluminum is easy to spot . BTW you probably won't find any worth even the face value on the coin. For example I have a 1983 UK 1 pound coin. Scammers on ebay and elsewhere show this as "rare" because of upside down rim stamp. It isn't upside down because they stamp the rim before the coin is stamped so it all depends on how it was fed into the machine. When I googled it AI showed that one sold for about $2000. They are worth their weight in scrap metal and not the value of 1£ in 1983.