Chert

Chert is a hard, fine-grained <a href="/facts/Sedimentary_rock/HQDCjrco">sedimentary rock</a> composed of <a href="/facts/Microcrystalline/5z8xALpK">microcrystalline</a> or <a href="/facts/Cryptocrystalline/4vlIFIzv">cryptocrystalline</a> <a href="/facts/Quartz/4n86tE2G">quartz</a>, the mineral form of <a href="/facts/Silicon_dioxide/A3WILp6J">silicon dioxide</a> (SiO2). Chert is characteristically of biological origin, but may also occur inorganically as a <a href="/facts/Precipitation_(chemistry)/s3BgsLLY">chemical precipitate</a> or a <a href="/facts/Diagenesis/F1nATwdp">diagenetic</a> replacement, as in <a href="/facts/Petrified_wood/JBu2j1N8">petrified wood</a>.
Chert is typically composed of the petrified remains of <a href="/facts/Siliceous_ooze/c6lp1dSv">siliceous ooze</a>, the biogenic sediment that covers large areas of the deep ocean floor, and which contains the silicon skeletal remains of <a href="/facts/Diatom/x2oEcP1P">diatoms</a>, <a href="/facts/Dictyochales/FoQTmquA">silicoflagellates</a>, and <a href="/facts/Radiolaria/j3SYzHCS">radiolarians</a>. <a href="/facts/Precambrian/zjF3N3Rx">Precambrian</a> cherts are notable for the presence of fossil <a href="/facts/Cyanobacteria/S8bKxIU9">cyanobacteria</a>. In addition to <a href="/facts/Micropaleontology/wES8f4as">microfossils</a>, chert occasionally contains <a href="/facts/Macrofossil/TKBySXyG">macrofossils</a>. However, some chert is devoid of any fossils.
Chert varies greatly in color, from white to black, but is most often found as gray, brown, grayish brown and light green to rusty red and occasionally as dark green. Its color is an expression of trace elements present in the rock. Both red and green are most often related to traces of iron in its <a href="/facts/Redox/Pyd5RVcj">oxidized and reduced</a> forms, respectively.

Chert open-in-new

Chert