Nahma junction, Isabella, Delta County, Michigan, USAi

Regional Level Types
Nahma junction	Quarry (Inactive)
Isabella	- not defined -
Delta County	County
Michigan	State
USA	Country

This location is approximately 3.3 miles north of Nahma Junction and 2.6 miles east of National Forest Highway 13 (NF-13).

The quarry is a small clearing in the forest and is basically a small (approximately ½ acre) excavation into the underlying bedrock. This location is not much of a quarry, as there has been very little excavation. Bedrock is exposed on the ground surface, with minimal vegetation growth.

The rocks exposed at this quarry are dolomitic facies of the early Silurian-aged Cabot Head Shale of the Cataract Group. The rocks here include gray, thin-bedded dolomite and gray to tan argillaceous shale and dolomite. The shale contains gypsum. This gypsum consists of thin layers along bedding planes and fractures throughout the shale, as well as small nodules. The thin layers of gypsum are of the “satin spar” variety and range from ¼” thick to over 2 inches in thickness. The thicker layers of satin spar gypsum are often formed into small domes on the quarry floor, where the gypsum layer is domed up several inches (and hollow beneath) in an area a foot or more in diameter.
White to cream colored nodules and lumps of fine-grained gypsum are also present. Crude crystals of clear selenite can be found, usually included with brown mud. These can be seen along cleavage surfaces of the crystals as the shale is broken apart.

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References