Sulfides from Mines and Deposits in the Herkimer Mining District

The term “sulfide” simply means the combination of sulphur with a metal, like iron.  Iron and sulphur combine to make pyrite, fools gold.  The iron and sulphur can also combine to make marcasite, which is sometimes used in jewlery.  Pyrite and marcasite are the most common sulfides in the Herkimer Mining District - if you can get to places where weathering has not been destructive and turned these minerals into lumps of rust. The “rust” remnants of these minerals are present in every mine, deposit, in the district (click on the weathering button for more information). Other sulfides come from combining different metals with sulphur -  combining with copper you get chalcopyrite, with zinc you get sphalerite. These are both present in the district and photos are included in the slide show below. Galena (lead + sulphur) has been reported and we will add a photo when we can.

Click on the button next - to see the seed crystal page

See the weathering page for examples of sulfides totally rusted

Variations in the Occurrence of Suflides

There are basically two episodes of sulfides that occur in the Herkimer Mining District. The first episode produced the largest amount, with large plates of pyrite and marcasite reaching up to 15 cm across  It is also common to find these plates much smaller, and they will curl. These pyrite/marcasite growths can also occurs as rods.  Both the rods and the plates have been found as inclusions within Herkimer diamonds. The rods and plates are covered with very small (less than a mm) pyrite (cubic) and marcasite (”cockscomb”) crystals. A rare form of pyrite has been found at HBQ where the pyrite occurs as pyritohedrons - the faces are pentagon shaped. Crystals of chalocpyrite are part of phase 1 and are very tiny (less than 1 mm). To the naked eye the difference is the brilliant gold shine that a cluster of these micro crystals produces. Sphalerite crystals are rare, but when found they are visible to the naked eye and have a reddish tint, like ruby sphalerite.  Poorly formed sphalerite in “seams” can also be found and often displays parallel growth. Galena has been reported, but not yet photographed.

The second episode of sulfides occurs as long prismatic crystals of marcasite.  The most common occurrence is as layers of “needles” in calcite that look gray or black.  Rust can also be on the same specimen.  These black “needles” can also be found as inclusions within Herkimer diamonds (see the inclusion page for more information).