Editing Desert varnish (section)

==Formation==
Desert varnish forms only on physically stable rock surfaces that are no longer subject to frequent [[precipitation (meteorology)|precipitation]], fracturing or [[ventifact|wind abrasion]]. The varnish is primarily composed of particles of [[clay]] along with [[oxidation|oxides]] of [[iron]] and [[manganese]].<ref>{{cite journal |last1=Perry |first1=Randall Stewart |last2=Adams |first2=John B. |title=Desert varnish: evidence for cyclic deposition of manganese |journal=Nature |date=November 1978 |volume=276 |issue=5687 |pages=489–491 |doi=10.1038/276489a0|bibcode=1978Natur.276..489P |s2cid=4318328 }}</ref>  There is also a host of trace elements and almost always some [[organic matter]]. The color of the varnish varies from shades of brown to black.<ref name=Chernicoff>{{cite book |last1=Chernicoff |first1=Stanley |last2=Whitney |first2=Donna |year=2007 |title=Geology: An Introduction to Physical Geology |edition=4th |publisher=Pearson Prentice Hall |page=585 |isbn=9780131751248}}</ref>

It has been suggested that desert varnish should be investigated as a potential candidate for a "[[shadow biosphere]]".<ref>{{cite journal |last1=Cleland |first1=Carol E. |title=Epistemological issues in the study of microbial life: alternative terran biospheres? |journal=Studies in History and Philosophy of Science Part C: Studies in History and Philosophy of Biological and Biomedical Sciences |date=December 2007 |volume=38 |issue=4 |pages=847–861 |doi=10.1016/j.shpsc.2007.09.007|pmid=18053938 }}</ref><ref>{{cite news |last=McKie |first=Robie |title=Life on Earth... but not as we know it |url=https://www.theguardian.com/science/2013/apr/14/shadow-biosphere-alien-life-on-earth |work=The Guardian |date=13 April 2013 |access-date=2022-02-25}}</ref> However, a 2008 microscopy study posited that desert varnish has already been reproduced with chemistry not involving life in the lab, and that the main component is actually silica and not clay as previously thought. The study notes that desert varnish is an excellent fossilizer for microbes and indicator of water. Desert varnish appears to have been observed by rovers on Mars, and if examined may contain fossilized life from Mars's wet period.<ref>{{cite journal |last1=Perry |first1=Randall |last2=Sephton |first2=Mark |title=Solving the mystery of desert varnish with microscopy |journal=Infocus |date=6 September 2008 |issue=11 |pages=62–76 |doi=10.22443/rms.inf.1.36 |doi-access=free}}</ref>