Why aren't minerals the same in all U.S. coins?

Answer 1

I assume you mean metals rather than minerals. When coins were first struck in various countries, the rule was generally that a coin had to contain enough metal to be worth the value indicated by its denomination, minus a slight amount for the government (called "seigniorage", effectively the government's profit on making the coin). The principle was that coins would have intrinsic value so everyone would be guaranteed that a particular coin was worth, and would buy, a specific amount.

In order to keep coins' sizes practical, small denominations were made of cheap metals such as copper and nickel, more valuable ones used silver, and the top end were made of gold. (It also meant that some smaller coins were more valuable than larger ones, because they used different metals.)

The principle of metal values worked for centuries, but as society developed and economies became more complicated, it was harder and harder for governments to control coins' values vs. their metal content. In the U.S. for ex., copper cents used to be the size of half-dollars, but by 1857 the price of copper had increased to the point where the old cents were replaced with coins about the size of modern cents. Later, as more gold and silver were discovered their relative prices fluctuated and coinage was adjusted again and again.

By 1933 all gold coins were withdrawn. Silver was kept, but in the 1960s its price shot up too. To preserve some order in coinage, silver was replaced with cupro-nickel, but there was an added glitch due to technology: new coins had to be compatible with old ones in vending machines, coin sorters, and so on. The new coins kept the same sizes and roughly the same weights. That's why dimes are still smaller than nickels or pennies, even though they're worth more.