Skarn

Skarn is an old Swedish mining term originally used to describe a type of silicate gangue, or waste rock, associated with iron-ore bearing sulfide deposits apparently replacing Palaeoproterozoic age limestones in Sweden's Persberg mining district. In modern usage the term "skarn" has been expanded to refer to calcium-bearing silicates of any age. In America the term "tactite" is often used synonymously with skarn.