File:Quartzose sandstone (Hinckley Sandstone, Neoproterozoic; Hinckley, Minnesota, USA) (23504564816).jpg

Quartz sandstone from the Precambrian of Minnesota, USA. (public display, Minnesota Discovery Center, Chisholm, Minnesota, USA)

Sandstone is the second most common sedimentary rock on Earth. It is a siliciclastic sedimentary rock composed of sand-sized particles, which are defined as grains between 2 millimeters and 1/16 of a millimeter. Most sandstones are dominated by quartz sand, but other common mineralogies include feldspar and lithic grains (= sand-sized rock fragments).

The sample shown above is a quartz arenite from the Hinckley Sandstone of Minnesota. This sandstone unit has 96% quartz. Quartz arenites are varieties of sandstone with more than 90% quartz. The rock is part of an extensive sedimentary deposit that filled the ancient Mid-Continent Rift System, a tectonic tear that formed about 1.1 billion years ago in the North American paleocontinent of Laurentia. It was similar to the modern-day East African Rift Valley, along which Africa is being ripped apart by the Afar Hotspot. The Mid-Continent Rift Valley extended from present-day Kansas to Lake Superior to lower Michigan to Ohio. Tectonic rifting started and ultimately stopped - it was a failed rift. Flood basalts were the earliest rocks to start filling the rift valley. The sandstone shown above was part of a post-volcanism sedimentary fill in the rift.

Isotopic dating of Hinckley Sandstone detrital zircon grains shows that several source areas were producing sediments. Hinckley zircons range in age from 1.115 Ga to 3.045 Ga (see Finley-Blasi, 2006). Even younger zircons (1.010 Ga) have been found in the underlying formation, the Fond du Lac Formation. This puts the maximum age of the Hinckley Sandstone at 1.01 billion years old and thus is likely early Neoproterozoic.

The Hinckley Sandstone is a significant groundwater aquifer in parts of Minnesota. The unit was also a major source of building stone (see link below for a vintage photo of an old sandstone quarry).

Stratigraphy: Hinckley Sandstone, Neoproterozoic

Locality: Hinckley, western Pine County, eastern Minnesota, USA

Some info. from:

Finley-Blasi (2006) - Detrital zircon age analysis of the Fond du Lac and Hinckley Sandstone Formations of northern Minnesota. pp. 132-135 in: Nineteenth Annual Keck Research Symposium in Geology Proceedings, April 20-23, 2006, Amherst, Massachusetts, USA.

Photos of Hinckley Sandstone outcrop & an old quarrying area: