1780 Austria coin?

What you have is an Austrian bullion coin. It probably dates much later, as they kept using dies of similar design. It is 0.833 fine (83%) silver and contains 0.7517 troy ounces of pure silver, which is worth $22 at today's market price. Dealers typically buy them at a dollar or two below that price, and sell them a little bit over. It's not rare, but a beautiful, classic design.