You can use silver for currency. You can even use pieces of coal or sticks of wood for currency. It doesn't matter, as long as the other side agrees to accept it as currency (and offer you what you would deem a fair value in return).
I personally don't care for silver as much as the silver bugs here. Claims of "undervalued" silver, relative to gold, have been around for decades. You would've thought that the free market would've allowed silver to shrink the silver/gold price ratio, no? Or are there other sinister, central banks artificially keeping the price of silver down for the last 40 years? And yeah, silver gets used by industry, but gold gets used for jewelry and store of wealth. The most common use for gold is class rings btw. Just cause one is used for machines doesn't mean demand will skyrocket. Much of that silver is recycled, the way copper is. People don't just throw it away once they're done with it. Hell, if we recycle aluminum, paper, and plastic, three of the cheapest materials in the world, we are obviously going to recycle silver.