Editing Chert (section)

==Prehistoric and historic uses==
Chert is of only modest economic importance today as a source of silica (quartz sand being much more important.) However, chert deposits may be associated with valuable deposits of [[iron]], [[uranium]], [[manganese]], [[phosphorite]], and [[petroleum]].{{sfn|Boggs|2006|p=206}} 

===Tools===
[[File:Mill Creek chert hoe and other artifacts Parkin HRoe 01.jpg|thumb|right|200px|[[Mill Creek chert]] from the [[Parkin Archeological State Park|Parkin Site]] in [[Arkansas]]]]

In prehistoric times, chert was often used as a raw material for the construction of [[stone tool]]s. Like [[obsidian]], as well as some [[rhyolite]]s, [[felsite]]s, [[quartzite]]s, and other [[tool stone]]s used in [[lithic reduction]], chert fractures in a [[Hertzian cone]] when struck with sufficient force. This results in [[conchoidal]] fractures, a characteristic of all minerals with no [[Cleavage (crystal)|cleavage]] planes. In this kind of fracture, a cone of force propagates through the material from the point of impact, eventually removing a full or partial cone, like when a plate-glass window is struck by a small object such as an [[air gun]] projectile. The partial Hertzian cones produced during lithic reduction are called [[lithic flake|flakes]], and exhibit features characteristic of this sort of breakage, including [[striking platform]]s, [[bulb of force|bulbs of force]], and occasionally [[eraillure]]s, which are small secondary flakes detached from the flake's bulb of force.<ref>{{cite journal |last1=Jennings |first1=Thomas A. |title=Experimental production of bending and radial flake fractures and implications for lithic technologies |journal=Journal of Archaeological Science |date=December 2011 |volume=38 |issue=12 |pages=3644–3651 |doi=10.1016/j.jas.2011.08.035|bibcode=2011JArSc..38.3644J }}</ref>

When a chert stone is struck against an iron-bearing surface, sparks result. This makes chert an excellent tool for starting fires, and both flint and common chert were used in various types of fire-starting tools, such as [[tinderbox]]es, throughout history. A primary historic use of common chert and flint was for [[flintlock]] [[firearms]], in which the chert striking a metal plate produces a spark that ignites a small reservoir containing [[black powder]], discharging the firearm.<ref name=":0" /><ref>{{cite journal |last1=Roets |first1=Michael |last2=Engelbrecht |first2=William |last3=Holland |first3=John D. |title=Gunflints and Musket Balls: Implications for the Occupational History of the Eaton Site and the Niagara Frontier |journal=Northeast Historical Archaeology |date=2014 |volume=43 |issue=1 |pages=189–205 |doi=10.22191/neha/vol43/iss1/10|doi-access=free }}</ref>

===Construction===

Cherts can cause several problems when used as concrete aggregates. Deeply weathered chert develops surface pop-outs when used in concrete that undergoes freezing and thawing because of the high porosity of weathered chert. The other concern is that certain cherts undergo an alkali-silica reaction with high-alkali cements. This reaction leads to cracking and expansion of concrete and ultimately to failure of the material.<ref>Terry R. West. "Geology Applied to Engineering," Waveland Press, 1995  {{ISBN|1577666550}}</ref>