{{Short description|Selenide of copper, thallium and silver}} {{Infobox mineral | name = Crookesite | category = Selenide mineral | boxwidth = | boxbgcolor = | image = File:Crookesite.jpg | imagesize = | caption = | formula = {{chem|Cu|7|(Tl|, Ag)|Se|4}} | IMAsymbol=Crk<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 = 2.BD.50 | system = Tetragonal | class = Disphenoidal ({{overline|4}}) <br/>H-M symbol: ({{overline|4}}) | symmetry = ''I''{{overline|4}} | color = Lead-gray | habit = As finely divided, disseminated specks, and as small veinlets. | twinning = | cleavage = Good, two at right angles | fracture = Brittle | mohs = 2.5–3 | luster = Metallic | refractive = | opticalprop = | birefringence = | pleochroism = | streak = | gravity = 6.90 | density = | melt = | fusibility = | diagnostic = | solubility = | diaphaneity = Opaque | other = | references = <ref name=Webmin>[http://webmineral.com/data/Crookesite.shtml Webmineral site]</ref><ref>[http://rruff.geo.arizona.edu/doclib/hom/crookesite.pdf Handbook of Mineralogy] </ref> }}
'''Crookesite''' is a selenide mineral composed of copper and selenium with variable thallium and silver.
==Characteristics== Its chemical formula is reported either as {{chem|Cu|7|(Tl|, Ag)|Se|4}} or {{chem|(Cu|, Tl|, Ag)|2|Se}}.<ref>{{Cite web |title=Crookesite |url=https://www.mindat.org/min-1159.html |access-date=2025-12-15 |website=www.mindat.org}}</ref> It is formed by precipitation from hydrothermal fluids, and contains by mass: 16.3% Tl, 47.3% Cu, 2.9% Ag, and 33.6% Se.<ref name=Webmin/>
Crookesite is an opaque, bluish grey to pink toned brown metallic mineral crystallizing in the tetragonal system. It has a Mohs hardness of 2.5 to 3 and a specific gravity of 6.9.
==Name and discovery== It was discovered in 1866 in Skrikerum, Sweden and named for Sir William Crookes (1832–1919), the discoverer of the element thallium.<ref name=Webmin/>
==See also== * List of minerals * List of minerals named after people * {{Annotated link|Sabatierite}}
==References== {{Reflist}} {{Refbegin}} * {{cite journal | doi = 10.1007/BF00815324 | title = Characterization of TlCu<sub>7</sub>S<sub>4</sub>, a crookesite analogue | year = 1987 | last1 = Berger | first1 = Rolf A. | last2 = Sobott | first2 = Robert J. | journal = Monatshefte für Chemie | volume = 118 | issue = 8–9 | pages = 967–972| s2cid = 102058943 }} * {{cite journal | doi = 10.1524/zkri.1987.181.1-4.241 | url = http://rruff.geo.arizona.edu/doclib/zk/vol181/ZK181_241.pdf | title =Crookesite and sabatierite in a new light. A crystallographer's comment | first = R..A. | last = Berger | journal = Zeitschrift für Kristallographie | year = 1987 | volume = 181| issue = 1–4 | pages = 241–249|bibcode = 1987ZK....181..241B }} {{Refend}}
Category:Silver minerals Category:Copper(I) minerals Category:Thallium minerals Category:Selenide minerals Category:Tetragonal minerals Category:Minerals in space group 82 Category:Minerals described in 1866
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