Mineral Habits of the C.E. Duff and Son Inc. Quarry

peridot with silver ring

At one time, the C.E. Duff and Son Inc. quarry near Huntsville, Ohio was one of the most heavily collected localities in the state of Ohio. Most knowledgeable mineral collectors recognize the Duff quarry as being famous for one mineral, Pyrite.

This locality has been noted for producing world class specimens of the species in a multitude of crystal forms. In fact, many would argue this to be one of the best world-wide localities for observing Pyrite crystal forms. For more than 30 years, Pyrite crystals from this locality have been a source of study for mineralogists and have been well documented and described on countless occasions.

Over the years, high quality specimens of Pyrite and other minerals were abundant and easily collected in the Southwest portion of the quarry. The shallow depth of the quarry and the uniformly horizontal bedding of the dolomite lend to a relatively safe collecting atmosphere.

In recent years, the operation has taken a new direction, opening a deeper, mostly unmineralized, second level. In addition, quarrying on the upper level has generally proceeded to the Northeast, away from the best mineralized zone into an area predominantly free of mineralization.

The combination of these factors caused recent collecting to be somewhat, but not completely, unproductive. Unfortunately, liability concerns, in this increasingly litigious age, have closed the door to current mineral collecting.


Pyrite and Dolomite on Dolostone



C.E. Duff and Son Inc. was founded in 1955, although aggregate mining around Huntsville can be traced back to the late 19th century. The current two level operation, owned by James E. Duff, is on the East side of State Route 117 just North of Huntsville, in Logan County. An earlier quarry, once owned by the Western Ohio Stone Co. and later by C.E. Duff and son Inc., was directly opposite the new operation and is now completely flooded.

Both quarries offered collectors with the same basic mineralization. Other than historical reference, little, if any, differentiation can be made between the minerals found in the older and newer quarries. The original quarry was much smaller than the current operation.

The general offices for C.E. Duff and Son Inc., located in front of the current quarry, are unmistakably marked by 2 large arches from the 1964 New York World’s Fair. C.E. Duff and Son Inc. also operates another limestone quarry near Kenton, in Hardin County, and several sand and gravel operations in the Bellefontaine area.

The company also owns and operates a number of Ohio Ready Mix Inc. plants in conjunction with the aggregate quarries. Several sons also operate related business near the Huntsville quarry.

Dolostone Mining

The dolomitic limestone, or dolostone, being mined at the C.E. Duff and Son Inc. Quarry in Logan County is of upper Silurian age and is recognized as a member of the Salina group. However, many parallels can be observed in the geologic features of this strata and the rocks in the Bluffton Stone Co. Quarry in Allen County, including raindrops, distinctive mudcracks and stromatolites.

These similarities lead to the conclusion that this dolostone is likely part of the Tymochtee formation. This strata lies just below the Columbus Limestone of Devonian age. Similar rocks and mineralization habits have also been observed in nearby operations including the quarry at Northwood, also in Logan County, and the quarry at York Center in Union County.

The material being quarried on the upper level is generally bluish gray in color and shale-like, ideal for flagstone. Due to the high levels of Iron in the strata, some of the thinner layers of the Dolomite are red in color. The lower level of the quarry houses a more dense and siliceous brownish gray material which is suitable for aggregate needs. Stone from this part of the quarry is typically void of mineralization or noticeable geologic features.


Although slight to moderate mineralization is evident throughout the C.E. Duff and Son Inc. quarry, commonly known to mineral collectors as “Duff’s”, the most aesthetic mineral specimens are generally found at the South end of the upper level. For the most part, mineralization occurs as crystals and crystalline masses lining or filling small pockets and crevices parallel to the bedding plane.

On average, most pockets range from 1 centimeter to 8 centimeters in size, but occasional larger pockets up to 25 centimeters have been observed. In the most productive areas, pockets are clustered together and typically have similar mineralogy. Often these pockets form in algal molds, stromatolites or under and along stylolites. Anhydrite nodules may also be responsible for some of the pockets at this locality.

Rare Anhydrite and Gypsum nodules have occasionally been observed. The C.E. Duff and Son Inc. quarry is generally considered to be near the boundary of the Findlay Arch Mineral District. This District is determined by the presence of brown Fluorite. Occasional brown Fluorite has been observed in various parts of the Quarry. Well formed brown, yellow, clear and purple Fluorite crystals are extremely rare and highly sought after from this classic locality.

The most common minerals found at the Duff quarry are Pyrite and Dolomite. Infrequent crystal specimens of Sphalerite and Calcite are also occasionally encountered throughout the quarry, although massive Calcite fillings are somewhat common. Some pockets also contain moderate to heavy amounts of Asphalt.

mining for minerals


Pyrite Mining

Without doubt, the C.E. Duff and Son Inc. quarry is the premier Ohio locality for Pyrite. While much larger crystalline Pyrite concretions are relatively abundant throughout the Devonian age Ohio Shale, quality specimens from this quarry are, in general, more aesthetic and in much higher demand.

At this classic locality, this relatively common sulfide mineral is known to develop numerous distinct crystal forms, often in association with Dolomite, Calcite and rarely Fluorite. Although many of the quarries in the Findlay arch mineral district occasionally produce specimens of the species, no other quarry in Ohio is noted for producing the abundance of good Pyrite specimens which the Duff quarry has turned out over the years.

The average Pyrite crystal from the C.E. Duff and Son Inc. quarry is quite small and well suited for micromounting. However, well formed crystals have been observed up to 2.5 centimeters from this locality. To the upper right is an example of large pyrite crystals for the locality. Large crystals are usually heavily distorted and irregular, occasionally showing multiple growth with more than one main crystal form.

Quality Pyrite specimens from this locality are highly valued by collectors of midwestern and Ohio minerals. In addition, many well respected world-wide mineral museums house pieces from this locality. These unique pyrite specimens are often naturally painted with a thin iridescent oxidation or tarnish which greatly enhances the aesthetics of this simple sulfide.

This iridescence has been observed in virtually every color of the rainbow. However, a quick wash with a toothbrush will return the crystals to a plain brassy yellow or silver color. The most aesthetic Pyrite specimens typically have some iridescence and are in association with Dolomite.