Like other fissure vein pieces of substance, this most likely dates to the 1870s-1890s peak of production and has a wonderful old antqiue patina to it. This particular piece is a rarity - a thick cluster of intergrown spinel-twinned copper crystals, to 6 cm in length! While common enough from Arizona, such thick twinned clusters are NOT common at all from Michigan's historic mines. The crystallization is complete all around, and the piece is much more impressive in person because the camera blurs on the focus here. Also, the patina on this is a very desirable chocolatey brown! Comes with custom lucite display base.