# Pearceite > Mediated Wiki article. Canonical URL: https://mediated.wiki/source/Pearceite > Markdown URL: https://mediated.wiki/source/Pearceite.md > Source: https://en.wikipedia.org/wiki/Pearceite > Source revision: 1301168971 > License: Creative Commons Attribution-ShareAlike 4.0 International (https://creativecommons.org/licenses/by-sa/4.0/) {{Infobox mineral | name = Pearceite | category = | boxwidth = 24 | boxbgcolor = | image = Pearceite-4jg57a.jpg | caption = Pearceite from [Butte](/source/Butte%2C_Montana), Montana, US | formula = {{chem2|Cu(Ag,Cu)6Ag9As2S11}}{{Cite web|url=http://rruff.info/ima/|title = IMA Mineral List with Database of Mineral Properties}} | IMAsymbol = Pea{{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}} | molweight = 2,096.80 g/mol | strunz = 2.GB.15 (10 ed)
2/E.05-20 (8 ed) | dana = 3.1.8.1 | system = [Monoclinic](/source/Monoclinic) or [trigonal](/source/trigonal) | symmetry = ''P{{overline|3}}m1'' (no. 164) | color = Black | habit = Pseudohexagonal prisms | twinning = | cleavage = {001} Poor{{Cite web|last1=Barthelmy|first1=David|year=2014|url=http://www.webmineral.com/data/Pearceite.shtml|access-date=7 August 2022|title = Pearceite Mineral Data|website=Webmineral.com}} | fracture = Conchoidal to irregular | tenacity = Brittle | mohs = 3 | luster = Metallic | refractive = 2.7 | opticalprop = Biaxial | birefringence = 2.7 | pleochroism = RL Pleochroism (in reflected plane polarised light): Very weak in air, fair in oil{{cite web |last1=Anthony |first1=John W. |last2=Bideaux |first2=Richard A. |last3=Bladh |first3=Kenneth W. |last4=Nichols |first4=Monte C. |title=Pearceite |url=http://www.handbookofmineralogy.org/pdfs/pearceite.pdf |website=Handbook of Mineralogy |publisher=Mineral Data Publishing |access-date=7 August 2022 |date=2005}} | streak = Black | gravity = 6.15 | melt = | fusibility = | diagnostic = | solubility = | diaphaneity = Opaque | other = Non-fluorescent, nonmagnetic, not radioactive | references = Gaines et al (1997) Dana’s New Mineralogy, Eighth Edition. Wiley{{mindat|id=3138|title=Pearceite|access-date=7 August 2022}}}} '''Pearceite''' is one of the four so-called "ruby silvers", pearceite {{chem2|Cu(Ag,Cu)6Ag9As2S11}}, [pyrargyrite](/source/pyrargyrite) {{chem2|Ag3SbS3}}, [proustite](/source/proustite) {{chem2|Ag3AsS3}} and [miargyrite](/source/miargyrite) {{chem2|AgSbS2}}. It was discovered in 1896 and named after Dr Richard Pearce (1837–1927), a Cornish–American chemist and metallurgist from [Denver](/source/Denver), Colorado. == Nomenclature == Pearceite and [polybasite](/source/polybasite) are closely related minerals that form the pearceite-polybasite series. Originally pearceite was thought to be an [arsenic](/source/arsenic) analogue of polybasite {{chem2|Cu(Ag,Cu)6Ag9Sb2S11}}, and was called arsenpolybasite, and one [polytype](/source/Polymorphism_(materials_science)) of polybasite was called antimonpearceite. Arsenpolybasite was found to represent two different polytypes, arsenpolybasite-221 and arsenpolybasite-222.{{cite journal | author=C. Frondel | date= 1963 | title= Isodimorphism of the polybasite and pearceite series | url= https://pubs.geoscienceworld.org/msa/ammin/article-abstract/48/5-6/565/542084/Isodimorphism-of-the-polybasite-and-pearceite | journal= American Mineralogist | volume= 48 | issue= 5–6 | pages= 565–572 | access-date= 2024-07-01 }} In modern usage the old name pearceite is replaced by the polytype name pearceite-Tac, arsenpolybasite-221 by pearceite-T2ac, arsenpolybasite-222 by pearceite-M2a2b2c and antimonpearcite by polybasite-Tac.{{cite journal |author1= L. Bindi | author2= M. Evain | author3= P.G. Spry |author4= S. Menchetti | year=2007 | title=The pearceite-polybasite group of minerals: Crystal chemistry and new nomenclature rules |journal= American Mineralogist |volume= 92 | issue= 5–6 |pages= 918–925 | doi= 10.2138/am.2007.2440 | bibcode= 2007AmMin..92..918B | url= https://pubs.geoscienceworld.org/msa/ammin/article-abstract/92/5-6/918/134492/The-pearceite-polybasite-group-of-minerals-Crystal | access-date= 2024-07-01| url-access= subscription }} Pearceite-Tac forms a series with polybasite-Tac. == Crystallography and Structure == Two structural varieties, [trigonal](/source/Trigonal_crystal_system) and [monoclinic](/source/Monoclinic_crystal_system), are known. The trigonal variety crystallizes in the [hexagonal scalenohedral class](/source/Trigonal_crystal_system) {{overline|3}}m ({{overline|3}} 2/m), [space group](/source/space_group) P{{overline|3}}m1 (P{{overline|3}} 2/m 1). The monoclinic variety crystallises in the [prismatic](/source/Monoclinic_crystal_system) 2/m class, space group C2/m. [Unit cell](/source/Unit_cell) parameters *Monoclinic variety: There are two formula units per unit cell (Z = 2), the lengths of the sides of the unit cell are a = 12.64 Å, b = 7.29 Å, c = 11.90 Å and the angle between the c and a directions is β = 90.0°. *Trigonal variety: There is one formula unit per unit cell (Z = 1), two of the sides are of equal length a = 7.3876 Å and the third side, parallel to the threefold axis, is c = 11.8882 Å. The crystal structure consists of sheets stacked along the c [axis](/source/Crystal_structure). The [arsenic](/source/arsenic) atoms form isolated {{chem2|(As,Sb)S3}} pyramids, [copper](/source/copper) [cations](/source/Ions) link two [sulfur](/source/sulfur) atoms and the [silver](/source/silver) cations are found in various sites with low [coordination number](/source/coordination_number)s, 2,3 and 4, as is usually the case with silver.{{cite journal | author1= L. Bindi | author2= M. Evain | author3=S. Menchetti | journal= Acta Crystallographica B | volume= 62 | date= 2006 | pages= 212–219 | title= Temperature dependence of the silver distribution in the crystal structure of natural pearcite, (Ag,Cu)16(As,Sb)2S11 | issue= Pt 2 | doi= 10.1107/S010876810600108X | pmid= 16552154 }} == Properties == Pearceite is often granular and massive; crystals are short, [tabular](/source/Crystal_habit) pseudo[hexagonal](/source/hexagonal) [prisms](/source/Prism_(geometry)) with bevelled edges, showing triangular striations on faces parallel to the plane containing the a and b [axes](/source/Crystal_axis), and rosettes of such crystals, to 3 cm across. The mineral is black, and in [polished section](/source/Thin_section) it is white with very dark red internal reflections. It has a black to reddish black [streak](/source/Streak_(mineralogy)) and a metallic [luster](/source/lustre_(mineralogy)), generally opaque, but translucent in very thin fragments. It is [biaxial](/source/Birefringence) with a very high [refractive index](/source/refractive_index) of 2.7 and maximum [birefringence](/source/birefringence) δ also 2.7. [Dispersion](/source/Birefringence) of the [optic axes](/source/Optic_axis_of_a_crystal) is relatively strong. Reflected light anisotropism is the property of appearing to change color when viewed under [crossed polarised light](/source/Polarization_(waves)) in a [reflected light microscope](/source/Thin_section). Pearceite exhibits moderate anisotropism, often dark violet. The color in reflected [plane polarised light](/source/Polarization_(waves)) is white, with very dark red internal reflections and very weak [pleochroism](/source/pleochroism) in air, fair in oil. [Reflectivity](/source/Reflectivity) in air at 540 nm is about 30%. It is not [fluorescent](/source/fluorescent). Pearceite is a brittle mineral that breaks with a [conchoidal](/source/Fracture_(mineralogy)) to irregular [fracture](/source/Fracture_(mineralogy)). It is soft, with [hardness](/source/Mohs_hardness) only 3, the same as [calcite](/source/calcite). The silver content gives it a high [specific gravity](/source/specific_gravity) of 6.15, the highest of the ruby silvers. [Cleavage](/source/Cleavage_(mineralogy)) is either absent or poor. The mineral is neither [magnetic](/source/magnetic) nor [radioactive](/source/radioactive). == Occurrence and associations == The [type locality](/source/Type_locality_(geology)) is the [Mollie Gibson Mine](/source/J_J_Hagerman), [Aspen](/source/Aspen%2C_Colorado), Aspen District (Roaring Fork District), [Pitkin County, Colorado](/source/Pitkin_County%2C_Colorado), where the mineral occurs in [hydrothermal deposits](/source/Vein_(geology)) formed at low to medium temperatures, associated with [acanthite](/source/acanthite), [tetrahedrite](/source/tetrahedrite), [native silver](/source/native_silver), [proustite](/source/proustite), [quartz](/source/quartz), [baryte](/source/baryte) and [calcite](/source/calcite). Type material is lodged at [Yale University](/source/Yale_University), New Haven, Connecticut, references 3.4270, 3.4292, 3.4293, and at The [Natural History Museum](/source/Natural_History_Museum%2C_London), London, England, reference 84843. ==References== {{reflist}} ==External links== * [http://www.microscopyu.com/articles/polarized/polarizedintro.html Nikon: Introduction to Polarized Light Microscopy] * [http://www.olympusmicro.com/primer/techniques/polarized/polarizedhome.html Olympus: Polarized Light Microscopy] {{Webarchive|url=https://web.archive.org/web/20090221172601/http://www.olympusmicro.com/primer/techniques/polarized/polarizedhome.html |date=2009-02-21 }} * [http://earth2geologists.net/Microscopes/index.htm Geological Microscopes] * [http://gerdbreitenbach.de/crystal/crystal.html A virtual Polarizing Microscope] {{Commons category}} Category:Sulfide minerals Category:Silver minerals Category:Copper(I) minerals Category:Arsenic minerals Category:Aluminium minerals Category:Trigonal minerals Category:Minerals in space group 164 Category:Monoclinic minerals Category:Minerals described in 1896 --- Adapted from the Wikipedia article [Pearceite](https://en.wikipedia.org/wiki/Pearceite) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Pearceite?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.