Image: Knife River Flint (Tertiary, North Dakota, USA) 8

Description: Flint (chert) from the Tertiary of North Dakota, USA. (tumble-polished) This is a sample of North Dakota's famous Knife River Flint, which was used by American Indians to make various tools. Flint, or chert (the two terms are synonymous, despite what anyone else says), is a cryptocrystalline, quartzose sedimentary rock. It can have a biogenic or chemical origin. Knife River Flint has not been identified in outcrop - it is only known as paleo-transported clasts. Pieces of this material can be found in Eocene-aged gravel deposits to Holocene surface lag deposits. It is possibly from a now-eroded correlative of a known horizon of silicified peat or lignite coal (!) called the HS Bed ("hard siliceous") (see Murphy, 2014). The HS Bed occurs in the Camels Butte Member of the Golden Valley Formation (Eocene). Locality: undisclosed site in North Dakota, USA

Referenced cited:

Murphy (2014) - Knife River Flint and other siliceous rocks in western North Dakota. North Dakota Department of Mineral Resources Geo News 41(1): 1-6. (www.dmr.nd.gov/ndgs/documents/newsletter/2014Winter/Winte...)
Author: James St. John
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