MINERALOGY OF THE HURON RIVER OIL SHALE FIRE

An oil shale fire has been burning in a cliff along the east side of the West Branch of the Huron River, Huron County, Ohio, for over a year. The site is located north of Monroeville near the intersection of River Road and Lamereaux Road in Ridgefield Township. The rock at the site is the Late Devonian Huron Shale, which contains: disseminated pyrite, beds of pyrite nodules, thin seams of coal, and over 10% disseminated organic matter. The site was investigated by geologists of the Ohio Geological Survey in December of 2009 (Larsen, 2010). The cause of the fire is unknown. The fire is about 90 m long, and probes operated by one of us (WS) have recorded temperatures as high as 427^oC at a depth of 0.46 m.

Vent mineralogy is one aspect of the environmental effects of the toxic gases emitted by oil shale fires whose condensation products pollute soils. Minerals of the vent area include: anhydrite, gypsum, halotrichite, sal ammoniac, orthorhombic sulfur, and tschermigite. These minerals are mostly sulfates, occurring on fragments of shale. Anhydrite is present in spherical white balls averaging 1 mm in diameter. Gypsum is white, occurring in 5 mm long bladed and smaller equant crystals. Halotrichite is found in fibrous silky white aggregates with individual crystals typically 0.5 mm long. Sal ammoniac occurs in colorless cubic crystals as large as 2 mm on an edge. Sulfur is found as pale yellowish brown skeletal bladed crystals 0.5 mm long. The tschermigite is vitreous and present as colorless to yellowish orange porous aggregates, individual crystals averaging 0.4 mm in diameter. The yellowish orange color is due to staining by iron oxide powder. The ammonia of the sal ammoniac and tschermigite presumably was derived from the vegetation caught up in the fire.