View source for Chemistry:Whewellite

{{Short description|Mineral}}
{{Infobox mineral
| name        = Whewellite
| boxwidth    =
| image       = Whewellite-md82a.jpg
| alt         =
| caption     = A white Whewellite crystal from Schlema, Germany
| category    = Oxalate minerals
| formula     = CaC<sub>2</sub>O<sub>4</sub>·H<sub>2</sub>O
| IMAsymbol   = Whe<ref>{{Cite journal|last=Warr|first=L.N.|date=2021|title=IMA–CNMNC approved mineral symbols|journal=Mineralogical Magazine|volume=85|issue=3|pages=291–320|doi=10.1180/mgm.2021.43|bibcode=2021MinM...85..291W|s2cid=235729616|doi-access=free}}</ref>
| molweight   =
| strunz      = 10.AB.45
| dana        =
| system      = [[Chemistry:Monoclinic|Monoclinic]]
| class       = Prismatic (2/m) <br /><small>(same [[Chemistry:H-M symbol|H-M symbol]])</small>
| symmetry    = ''P2<sub>1</sub>/c'' (no. 14)
| unit cell   =
| color       = Colorless, yellowish, brownish
| colour      =
| habit       = Equant or stout prismatic crystals
| twinning    = ''e'' {<nowiki/>{{overline|1}}01} twin plane
| cleavage    = {<nowiki/>{{overline|1}}01} good, {010} imperfect, {001} indistinct, {110} indistinct
| fracture    = Conchoidal
| tenacity    = Brittle
| mohs        = 2.5–3
| luster      = Vitreous to pearly
| streak      =
| diaphaneity = Transparent
| gravity     = 2.23
| density     =
| polish      =
| opticalprop = Biaxial (+), colorless (transmitted light)
| refractive  =
| birefringence =
| pleochroism =
| 2V          =
| dispersion  =
| extinction  =
| length fast/slow =
| fluorescence =
| absorption  =
| melt        =
| fusibility  =
| diagnostic  =
| solubility  = Insoluble in water, soluble in acids
| impurities  =
| alteration  =
| other       =
| prop1       =
| prop1text   =
| references  = <ref name="mindat">[http://www.mindat.org/min-4276.html Whewellite: mindat.org]</ref><ref>[http://www.webmineral.com/data/Whewellite.shtml Webmineral.com]</ref><ref>[http://www.handbookofmineralogy.com/pdfs/whewellite.pdf ''Handbook of Mineralogy'']</ref><ref>{{cite journal |last1=Tazzoli |first1=V. |last2=Domeneghetti |first2=M.C. |journal=American Mineralogist |volume=65 |year=1980 |pages=327–334 |title=The crystal structures of whewellite and weddellite: re-examination and comparison |url=https://pubs.geoscienceworld.org/msa/ammin/article-abstract/65/3-4/327/41138/The-crystal-structures-of-whewellite-and?redirectedFrom=fulltext |access-date=31 December 2020}}</ref>
}}

'''Whewellite''' {{IPAc-en|ˈ|h|juː|ə|l|aɪ|t}} is a mineral, hydrated [[Chemistry:Calcium oxalate|calcium oxalate]], formula [[Chemistry:Calcium|Ca]] [[Chemistry:Carbon|C]]<sub>2</sub>[[Chemistry:Oxygen|O]]<sub>4</sub>·[[Chemistry:Water|H<sub>2</sub>O]]. Because of its organic content it is thought to have an indirect biological origin; this hypothesis is supported by its presence in [[Earth:Coal|coal]] and sedimentary [[Earth:Nodule (geology)|nodules]]. However, it has also been found in hydrothermal deposits where a biological source appears improbable. For this reason, it may be classed as a true mineral.

Whewellite, or at least crystalline calcium oxalate, does also arise from biological sources.  Small crystals or flakes of it are sometimes found on the surfaces of some cacti, and kidney stones frequently have the same composition.

Whewellite was named after [[Biography:William Whewell|William Whewell]] (1794–1866), an {{wipe|England}} [[History:Polymath|polymath]], [[Earth:Natural history|naturalist]] and [[Scientist|scientist]], professor of moral philosophy at Cambridge and inventor of the system of crystallographic indexing.<ref name="mindat"/>

==Heat decomposition==
[[Image:whewellite tga.jpg|thumb|left|300px|Whewellite (calcium oxalate monohydrate) heat decomposition mass curve. The whewellite decomposes first to anhydrous calcium oxalate, then to calcium carbonate (losing carbon monoxide), and finally to calcium oxide (losing carbon dioxide).]]
Whewellite is used as a [[Chemistry:Thermogravimetric analysis|thermogravimetric analysis]] standard due to its well-known decomposition temperatures and products.

== See also ==
* List of minerals recognized by the International Mineralogical Association
* [[Earth:List of minerals named after people|List of minerals named after people]]

==References==
{{reflist}}

==Bibliography==
*<small>Palache, P.; Berman H.; Frondel, C. (1960). "''Dana's System of Mineralogy, Volume II: Halides, Nitrates, Borates, Carbonates, Sulfates, Phosphates, Arsenates, Tungstates, Molybdates, Etc. (Seventh Edition)"'' John Wiley and Sons, Inc., New York, pp. 1099–1101.</small>

[[Category:Calcium minerals]]
[[Category:Oxalate minerals]]
[[Category:Monoclinic minerals]]
[[Category:Minerals in space group 14]]


{{Sourceattribution|Whewellite}}