The very first thing you have to know are the two types of silver most commonly traded silver bars and silver coins. Silver bars are pretty common but there are a few characteristics of bars that make them less desirable as coins. The first reason is that bars are less prestigious as bars. When trading, coins can be bought and sold much easier than bars. Besides, with bars you have to sell the whole thing in order to liquidate. Either you sell everything or nothing at all. It is an all-or-nothing situation with bars. Silver coins clearly do not have this problem.
The fact that they are government-minted and can be broken up into smaller quantities are the main reasons for the preference of coins. There is also the universality of acceptance of coins that make them attractive. Even when silver prices fluctuate wildly, there will be little question to government-minted coins. Their value practically stays the same way on the market. An assay, or scientific measurement of silver in a coin or bar, is also less likely to happen when you trade in coins.