Superior Swirl/Pioneer Swirl slag glass is a very unique lapidary material, from upper peninsula of Michigan, which displays a subtle play of swirling patterns in multiple shades of blue. It is technically a glassy slag left from a copper smelting mining process that was active throughout the 1800 – 1900”s. There are multiple collecting sites for similar material; Leeland Blue from the lower peninsula, Sieber Agate from Germany, and Swedish Blue. It characteristically contains numerous pinhead sized vesicles and works up much the same as obsidian. It produces distinctive cabs ideal for that “special” finished piece.