From the Eagle Mine, in Gilman, Colorado

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Named after Marmato mining district in Colombia, Marmatite is an opaque, black, iron-rich variety of Sphalerite. It has a hardness of 3½ – 4 and a specific gravity of 3.9-4.1. It’s found in more than 25,396 recorded localities on Mindat, and according to Wikipedia, it’s amongst the most common sulfide minerals, found worldwide in a variety of deposit types, including skarns, hydrothermal deposits, sedimentary beds, volcanogenic massive sulfide deposits (VMS), Mississippi-valley type deposits (MVT), granite and coal.

Sphalerite has a breakdown on WebMineral of 64% Zinc, 33% Sulfur, and 3% Iron, but Marmatite, specifically, has up to 25% Iron, according to Wikipedia. Also from Wikipeida, Sphalerite “is an important ore of zinc; around 95% of all primary zinc is extracted from sphalerite ore. However, due to its variable trace element content, sphalerite is also an important source of several other metals such as cadmium, gallium, germanium, and indium which replace zinc.” While it’s not an expensive Tsumgallite or Cadmoindite, it’s still a great representation of some rare elements for element collectors, but this is likely even more valued by Colorado mineral collectors!

This rock has been mined and utilized for possibly 1,400 years or longer for brass, bronze, and so many more useful metals, and while it’s not Gold or Silver, it’s still been a prize and main mineral mined from by many Colorado miners! Be sure to keep your eyes out for a rock like this and you might just discover a new Zinc mine!


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