Tuff
Tuff is a pyroclastic rock composed mostly of angular fragments of volcanic material deposited from the air. If deposited on land while hot, the particles weld together as a welded tuff; otherwise, normal lithification occurs.
In Arkansas, two tuff units are present. The Hatton tuff lentil of the Stanley Shale (Mississippian) is exposed in Polk County. Southwest of the community of Hatton, the tuff has a maximum thickness of 300 to 400 feet, but 90 feet is more common. The tuff is massive, homogeneous, and jointed so that determination of bedding is difficult. The unweathered fine-grained rock is dark gray and may appear spotted due to light-colored feldspar crystals. Under the microscope, numerous broken volcanic glass fragments (shards) compose much of the rock. The unweathered rock is tough, compact, and may contain Late Pennsylvanian milky quartz veins. Tuff beds are also present in southwest Arkansas in the Woodbine Formation (Cretaceous), but have no resource potential for aggregate.
The Hatton tuff has now begun to see use in Arkansas as an aggregate as fresher portions of the deposits near Hatton, Polk County, are mined. It was previously shipped to and continues to be an available concrete aggregate resource for east Texas. The Hatton also has potential as a cementing agent.
References
Honess, C. W., 1923, Geology of the southern Ouachita Mountains of Oklahoma: Oklahoma Geological Survey Bulletin 32, part 1, 278 p.
Miser, H. D., and Purdue, A. H., 1929, Geology of the DeQueen and Caddo Gap quadrangles, Arkansas: U. S. Geological Survey Bulletin 808, 195 p.
Williams, J. F., 1891, The igneous rocks of Arkansas: Arkansas Geological Survey Annual Report for 1890, v. II, 457 p.