Cash does not have an inherent value. If it did, money markets wouldn't exist because all cash would have an inherent value, and that would not change. Even gold and silver don't have an inherent value. If I'm starving and I have something to trade for food and you're the only person around, I'm not going to trade for your silver or gold if I need food. At that time, food has a value to me, while precious metals do not.
Valuing something in a given currency a learned skill. When aboriginal tribes were forcibly assimilated into Australian society, one of the most difficult things for many of them to learn was how money worked. I read a while back about one person who walked into a grocery store soon after being brought into the city, picked up a couple of things from a shelf, and walked out, not understanding why people were shouting at and chasing him.
Similarly, what if I plopped down a coin made of palladium. Could you spot its inherent value if the language on the coin wasn't familiar to you? Would you place its value higher or lower than silver if you didn't know it was made of palladium?
Your coworkers were probably just amazed to see some silver coins only because they're not used to seeing them. If you took them into most stores, you wouldn't be able to spend them, even if they were US silver coins because people wouldn't be familiar with them. Hopefully, they wouldn't call the cops on you like some do for $2 bills, but they might refuse the transaction to avoid the risk of falling for a scam.