Sphalerite; (Zn,Fe)S

sphalerite

One of the most highly sought sulfide species by Ohio mineral collectors is sphalerite. Sphalerite has greater appeal to most serious Ohio collectors than pyrite and marcasite and is more frequently encountered, and therefore more obtainable, than other sulfide minerals such as galena. Commonly, Ohio sphalerite specimens consist of sharp wine red, orange or black crystals on limestone or dolostone matrix which with few exceptions are of identical form and cannot be differentiated by locality.

At the Monroeville locality, rare examples of crude, rounded, multigrowth brown to black crystals up to 2 centimeters on ferroan dolomite have been observed. These crystals, though less distinct than sphalerite crystals from most Ohio limestone and dolostone quarries, are more unique. The sphalerite was deposited some time after the 4th generation of ferroan dolomite, though its exact place in the sequence cannot be pinpointed.

It should be noted that most septaria will not produce sphalerite and those few which do may have only one or two isolated crystals. It is likely that sphalerite crystals may occur differently than those in the photos to the left and right, as an insufficient number of examples have been recovered to make any broader generalizations.

Thin seams, milky white masses and crude, often partially dissolved, crystals of whewellite are rarely found at the Monroeville locality. This substance is more commonly found in septaria a few kilometers to the north along the Huron River near Milan in Erie County. Mineral collectors disagree on the validity of whewellite as a true mineral species, as the substance has organic components in its formula.

The mineral purist would completely discount whewellite because of the organic connection. In fact, whewellite is known to form quite rapidly on decaying saguaro cactus and agave plants in Arizona. It is also the chief component of kidney stones. In these instances, the compound would be better described as a bio-mineral, because of the non-geological development. However, the compound has also been reported in hydrothermal veins, where living matter is not present. In this situation, it is more likely a true mineral because it is formed with no biological connection and has a set chemical formula.

At the Monroeville locality, whewellite is directly linked with biological matter, namely fossilized arthrodire bones. Although the substance precipitated in a geological environment, its origin stems from organic matter and therefore classifying it as a valid mineral is not entirely correct. Legitimacy aside, at best this locality yields unappealing specimens of whewellite.