Hornblende

2025-07-24T11:01:54Z

2607:EA00:107:2007:6D74:82D0:FED5:7C9E: /* Etymology */Removed incorrect apostrophe

{{Short description|Complex inosilicate series of minerals}}
{{Infobox mineral
| name = Hornblende
| category = Silicate mineral
| boxwidth =
| boxbgcolor =
| image = Apatite-(CaOH)-Hornblende-38354.jpg
| caption = Hornblende crystal (dark green) about 35 mm long, with [[apatite]] (white)
| formula = {{chem2|Ca2(Mg,Fe,Al)5(Al,Si)8O22(OH)2}}
| IMAsymbol = Hbl<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 =
| color = Black to dark green or brown
| habit = Hexagonal/granular
| system = [[Monoclinic]]
| symmetry = ''C2/m''
| twinning =
| cleavage = Imperfect at 56° and 124°
| fracture = Uneven
| mohs = 5–6
| luster = Vitreous to dull
| refractive =
| opticalprop =
| birefringence =
| pleochroism = Strong
| streak = Pale gray, gray-white,<ref name=mindatFe>{{mindat|id=1519|title=Ferrohornblende}}</ref><ref name=mindatMg>{{mindat|id=2524.html|title=Magnesiohornblende}}</ref> white, colorless<ref>{{Cite web|url=https://geology.com/minerals/hornblende.shtml|title=Hornblende Mineral | Uses and Properties}}</ref>
| gravity = 2.9
| melt =
| fusibility =
| diagnostic =
| solubility =
| diaphaneity =
| other =
| references = <ref>{{cite journal |last1=Phillips |first1=M.W. |last2=Draheim |first2=J.E. |last3=Popp |first3=R.K. |last4=Clowe |first4=C.A. |last5=Pinkerton |first5=A.A. |journal=American Mineralogist |volume=74 |year=1989 |pages=764–773 |title=Effects of oxidation-dehydrogenation in tschermakitic hornblende |url=https://pubs.geoscienceworld.org/msa/ammin/article-abstract/74/7-8/764/42278/Effects-of-oxidation-dehydrogenation-in?redirectedFrom=fulltext |access-date=30 December 2020}}</ref>
}}

'''Hornblende''' is a complex [[silicate minerals#Inosilicates|inosilicate]] series of [[mineral]]s.<ref>{{mindat|id=8789.html|title=Hornblende Root Name Group}}</ref> It is not a recognized mineral in its own right, but the name is used as a general or field term, to refer to a dark [[amphibole]]. Hornblende minerals are common in [[Igneous rock|igneous]] and [[metamorphic rock]]s.

The general formula is {{chem2|(Ca,Na)_{2–3}(Mg,Fe,Al)5(Al,Si)8O22(OH,F)2}}.

== Physical properties ==
Hornblende has a [[Mohs scale of mineral hardness|hardness]] of 5–6, a [[specific gravity]] of 3.0 to 3.6, and is typically an opaque green, dark green, brown, or black color. It tends to form slender prismatic to bladed crystals, diamond-shaped in cross section, or is present as irregular grains or fibrous masses.<ref name=Nesse2000>{{cite book |last1=Nesse |first1=William D. |title=Introduction to mineralogy |date=2000 |publisher=Oxford University Press |location=New York |isbn=9780195106916 |pages=285–286}}</ref>

Its planes of [[cleavage (crystal)|cleavage]] intersect at 56° and 124° angles. Hornblende is most often confused with the [[pyroxene]] series and [[biotite|biotite mica]], which are also dark minerals found in [[granite]] and [[charnockite]]. Pyroxenes differ in their cleavage planes, which intersect at 87° and 93°.<ref>{{cite book |title=A Field Guide To Rocks and Minerals |last=Pough |first=Frederick H. |publisher=Houghton Mifflin |location=Boston |year=1976 |edition=4 |page=249}}</ref>

Hornblende is an inosilicate (chain silicate) mineral, built around double chains of silica tetrahedra. These chains extend the length of the crystal and are bonded to their neighbors by additional metal ions to form the complete crystal structure.{{sfn|Nesse|2000 |p=277–279}}

== Compositional variances ==
Hornblende is part of the calcium-amphibole group of amphibole minerals.{{sfn|Nesse|2000|p=278}} It is highly variable in composition, and includes at least five solid solution series:

* [[Magnesiohornblende]]–[[ferrohornblende]], {{chem2|Ca2[(Mg,Fe)4Al]Si7AlO22(OH)2}}
* [[Tschermakite]]–[[ferrotschermakite]], {{chem2|Ca2[(Mg,Fe)3Al2]Si6Al2O22(OH)2}}
* [[Edenite]]–[[ferroedenite]], {{chem2|NaCa2(Mg,Fe)5Si7AlO22(OH)2}}
* [[Pargasite]]–[[ferropargasite]], {{chem2|NaCa2[(Mg,Fe)4Al]Si6Al2O22(OH)2}}
* [[Magnesiohastingstite]]–[[hastingsite]], {{chem2|NaCa2[(Mg,Fe)4Fe^{3+}]Si6Al2O22(OH)2}}

[[File:Ferrohornblende-4aa53a.jpg|thumb|Ferrohornblende, near Bilin, [[ Bohemia]], Czech Republic]]
In addition, [[titanium]], [[manganese]], or [[chromium]] can substitute for some of the cations and oxygen, [[fluorine]], or [[chlorine]] for some of the [[hydroxide]] (OH). The different chemical types are almost impossible to distinguish even by optical or X-ray methods, and detailed chemical analysis using an electron microprobe is required.{{sfn|Nesse|2000|p=285}}

There is a solid solution series between hornblende and the closely related amphibole minerals, [[tremolite]]–[[actinolite]], at elevated temperature. A [[miscibility gap]] exists at lower temperatures, and, as a result, hornblende often contains exsolution lamellae of [[grunerite]].<ref>{{cite book |last1=Klein |first1=Cornelis |last2=Hurlbut |first2=Cornelius S. Jr. |title=Manual of mineralogy : (after James D. Dana) |date=1993 |publisher=Wiley |location=New York |isbn=047157452X |edition=21st |pages=496–497}}</ref>

==Occurrence==
[[File:Horndio.jpg|thumb|Hornblende [[diorite]] from the [[Henry Mountains]], Utah, US]]
[[File:Schist (Ordovician; Marlboro West Route 9 roadcut, Vermont, USA) 2.jpg|thumb|Ordovician hornblende schist near [[Marlboro, Vermont]]. The black sprays are hornblende amphibole.]]
Hornblende is a common constituent of many [[igneous rock|igneous]] and [[metamorphic rocks]] such as [[granite]], [[syenite]], [[diorite]], [[gabbro]], [[basalt]], [[andesite]], [[gneiss]], and [[schist]]. It crystallizes in preference to pyroxene minerals from cooler magma that is richer in silica and water.{{sfn|Nesse|2000|p=279}}

It is the principal mineral of [[amphibolite]]s, which form during medium- to high-grade [[metamorphism]] of [[mafic]] to [[intermediate composition|intermediate]] igneous rock (igneous rocks with relative low silica content) in the presence of pore water. Much of the pore water comes from the breakdown of [[mica]]s or other hydrous minerals. However, hornblende itself breaks down at very high temperatures.{{sfn|Nesse|2000|p=279}} Hornblende alters easily to [[chlorite group|chlorite]], [[biotite]], or other mafic minerals.{{sfn|Nesse|2000|p=286}}

A rare variety of hornblende contains less than 5% of [[iron oxide]], is gray to white in color, and is named [[edenite]] from its locality in Edenville, [[Orange County, New York]].

[[Oxyhornblende]] is a variety in which most of the iron has been oxidized to the [[ferric]] state, {{chem2|Fe^{3+}|}}. Charge balance is preserved by the substitution of oxygen ions for hydroxide. Oxyhornblende is also typically enriched in titanium. It is found almost exclusively in volcanic rock and is sometimes called ''basaltic hornblende''.<ref>{{cite book |editor1-last=Jackson |editor1-first=Julia A. |title=Glossary of geology. |date=1997 |publisher=American Geological Institute |location=Alexandria, Virginia |isbn=0922152349 |edition=Fourth |chapter=basaltic hornblende}}</ref>{{sfn|Nesse|2000|p=285–286}}

==Etymology==
The word ''hornblende'' is believed to derive from [[German language|German]] {{lang|de|Horn}} ('horn') and {{lang|de|blende}} ('deceive'), in allusion to its similar appearance to metal-bearing ore minerals,<ref name=HBM>{{cite web |last1=Anthony |first1=John W. |last2=Bideaux |first2=Richard A. |last3=Bladh |first3=Kenneth W. |last4=Nichols |first4=Monte C. |title=Ferrohornblende |url=http://www.handbookofmineralogy.org/pdfs/ferrohornblende.pdf |archive-url=https://web.archive.org/web/20110822184146/http://www.handbookofmineralogy.org/pdfs/ferrohornblende.pdf |archive-date=2011-08-22 |url-status=live |website=Handbook of Mineralogy |publisher=Mineral Data Publishing |access-date=14 March 2022 |date=2005}}</ref> or ('to blind') referring to its lustre.<ref>{{Cite book |last=Cook |first=David |title=Pocket Guide - Rocks and Minerals |last2=Kirk |first2=Wendy |publisher=Larousse |year=1995 |isbn=0752300091 |publication-place=London |page=110 |orig-year=1991}}</ref>

== See also ==
* {{annotated link|List of minerals}}

==References==
{{Commons category|Hornblende}}
{{Reflist}}

{{Authority control}}

[[Category:Inosilicates]]
[[Category:Calcium minerals]]
[[Category:Iron minerals]]
[[Category:Magnesium minerals]]
[[Category:Aluminium minerals]]
[[Category:Monoclinic minerals]]
[[Category:Minerals in space group 12]]
[[Category:Blendes]]

[[de:Amphibolgruppe#Calcium-Amphibole]]

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Hornblende