Melvin Stone quarry, Crownover Mill, Pickaway County, Ohio, USAi

Regional Level Types
Melvin Stone quarry	Quarry (Active)
Crownover Mill	- not defined -
Pickaway County	County
Ohio	State
USA	Country

LOCALITY
Limestone quarry, located 1 mile east of town.
Details about this open pit quarry’s geology and mineralogy are listed in Maertens (2018).

The Williamsport Plant is the active mining portion, east pit, on the left bank of the Deer Creek. The plant is located in Pickaway County, Ohio, United States of America.
Calcite crystals can be found in the Delphi member in the upper division of the Columbus Limestone of Emsian-Eifelian age in the Middle Devonian Wabash Platform. The limestone beds are highly calcareous semicrystalline gray limestone, evenly bedded; very fossiliferous and massive; irregular, and indistinctly separated. They contain small masses of chert and pockets of calcite crystals. As a rule, the layers show little signs of crystallization, but some blocks glisten with calcite cleavage faces. Fresh rock has a petroliferous odor.

CALCITE
Calcite is the most abundant mineral in the Devonian rocks at Williamsport quarry. Abundant is a relative expression, as the actual occurrence of collectible calcite crystals depends mostly on spaces to grow and on accessible rock during the surveys of the active quarry. Multiple surveys resulted in few occurrences of collectible specimens and it is rare to find specimens for sale. The Vasichko family advises this quarry provides one of the widest set of calcite forms in Ohio (Joe Vasichko, personal communication, 2022).

During a survey in 2022, the first level in the quarry, exposed the top of the bedrock limestone. The overlying Wisconsin age drift and till and Olentangy Shale (upper and Middle Devonian) were excavated, exposing a thin iron sulfide (pyrite and marcasite) layer at the unconformable contact between the shale and limestone, visible as patches of rusty red to orange yellow stained rock. The exposed top contact zone of the Columbus Limestone appeared mostly flat and near horizontal. The bench walls exposed occasional small local dips / synclines without karstic features.
The north-east section of the bench exposed small mounds of limestone conforming to the Columbus Limestone These shallow mounds are one to two meters high and round to out of round with a diameter to 10 meters, although most are smaller. There is a shallow 30 to 50 cm depression around the mounds.
The exact origin of these mounds is unknown. Pyrite heave is excluded because the iron sulfides lay on top of the limestone mounds and the sulfides content in the rather pure limestone is deemed insufficient. No related voids from dissolved secondary gypsum (iron sulfide decomposition product) were observed. The mounds are too small to be considered carbonate mud mounds and no observations point to algal, stromatoporoid and other microbial mediated process mounds. No brecciation was observed in the rock, feature of lithified limestone deformation. The author assumes that these mounds may originate during sediment compaction and early cementing to lithification but more likely they are the result from surface weathering of the limestone prior to being buried under the shale. Mark Peter of the ODNR hints to the latter origin of the mounds (Scott Kell, personal communication, 2022).
The marine fossiliferous gray limestone rock of the mounds contains thin fractures to 10 mm wide, similar to the underlying rock, that are filled by massive white calcite. There is minor massive pyrite and marcasite fill in some sections of these veins.
Exploration of one mound revealed a wider open vein – exposed at the surface near the top of the mound - lined with euhedral calcite crystals. The vein with variable width, from 10 to 50 mm, contained occasional wider vugs with calcite crystallization. The origin is assumed to be of the crack-seal vein type, probably widened through limestone dissolution.

Other Regions, Features and Areas containing this locality

References