Editing Concretion (section)

===Kansas pop rocks===

Kansas pop rocks are concretions of either iron sulfide, ''i.e.'' [[pyrite]] and [[marcasite]], or in some cases [[jarosite]], which are found in outcrops of the [[Smoky Hill Chalk|Smoky Hill Chalk Member]] of the Niobrara Formation within [[Gove County, Kansas]]. They are typically associated with thin layers of altered volcanic ash, called [[bentonite]], that occur within the [[chalk]] comprising the Smoky Hill Chalk Member. A few of these concretions enclose, at least in part, large flattened valves of inoceramid [[bivalve]]s. These concretions range in size from a few millimeters to as much as {{convert|0.7|m|ft|abbr=on|sp=us}} in length and {{convert|12|cm|ft|abbr=on|sp=us}} in thickness. Most of these concretions are [[oblate spheroid]]s. Other "pop rocks" are small polycuboid pyrite concretions, which are as much as {{convert|7|cm|ft|abbr=on|sp=us}} in diameter. These concretions are called "pop rocks" because they explode if thrown in a fire. Also, when they are either cut or hammered, they produce sparks and a burning sulfur smell. Contrary to what has been published on the Internet, none of the iron sulfide concretions, which are found in the Smoky Hill Chalk Member were created by either the replacement of fossils or by metamorphic processes. In fact, [[metamorphic rocks]] are completely absent from the Smoky Hill Chalk Member.<ref name=Hattan>{{cite journal |last1=Hattin |first1=D.E. |year=1982 |title=Stratigraphy and depositional environment of the Smoky Hill Chalk Member, Niobrara Chalk (Upper Cretaceous) of the type area, western Kansas |journal=Kansas Geological Survey Bulletin |volume=225 |pages=1–108}}</ref> Instead, all of these iron sulfide concretions were created by the precipitation of iron sulfides within anoxic marine [[pelagic sediments|calcareous ooze]] after it had accumulated and before it had [[Lithification|lithified]] into chalk.
[[File:Marleka fairy stone from Stensö in Sweden.JPG|thumb|''Marleka'' fairy stone from Stensö in Sweden]]

Iron sulfide concretions, such as the Kansas Pop rocks, consisting of either [[pyrite]] and [[marcasite]], are nonmagnetic.<ref>{{cite journal |last1=Hobbs |first1=D |last2=Hafner |first2=J |title=Magnetism and magneto-structural effects in transition-metal sulphides |journal=Journal of Physics: Condensed Matter |date=25 October 1999 |volume=11 |issue=42 |pages=8197–8222 |doi=10.1088/0953-8984/11/42/303|bibcode=1999JPCM...11.8197H |s2cid=250900204 }}</ref> On the other hand, iron sulfide concretions, which either are composed of or contain either [[pyrrhotite]] or [[smythite]], will be magnetic to varying degrees.<ref>{{cite journal |last1=Hoffmann |first1=Viktor |last2=Stanjek |first2=Helge |last3=Murad |first3=Enver |title=Mineralogical, magnetic and mössbauer data of symthite (Fe9S11) |journal=Studia Geophysica & Geodætica |date=December 1993 |volume=37 |issue=4 |pages=366–381 |doi=10.1007/BF01613583|bibcode=1993StGG...37..366H |s2cid=131123088 }}</ref> Prolonged heating of either a pyrite or marcasite concretion will convert portions of either mineral into pyrrhotite causing the concretion to become slightly magnetic.