Editing Prehnite

{{Short description|Inosilicate of calcium and aluminium}}
{{Infobox mineral
| name        = Prehnite
| category    = [[Silicate mineral]]
| image       = Prehnite - Southbury, Connecticut, USA.jpg
| caption     = 
| formula     = Ca<sub>2</sub>Al(AlSi<sub>3</sub>O<sub>10</sub>)(OH)<sub>2</sub>
| IMAsymbol   = Prh<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>
| strunz      = 9.DP.20 <br/>(Inosilicate transitional to phyllosilicate)
| dana        = 72.1.3.1 <br/>(Phyllosilicate)
| system      = [[Orthorhombic]] 
| class       = Pyramidal (mm2) <br/><small>(same [[H-M symbol]])</small>
| symmetry    = ''P2cm''
| color       = Colorless to gray to yellow, yellow-green or white
| habit       = Globular, reniform to stalactitic
| twinning    = Fine lamellar
| cleavage    = Distinct on [001]
| fracture    = 
| tenacity    = Brittle
| mohs        = 6–6.5
| luster      = Vitreous to pearly
| streak      = White
| diaphaneity = Semi-transparent to translucent
| gravity     = 2.8–2.95
| density     = 
| polish      = 
| opticalprop = Biaxial (+)
| refractive  = nα = 1.611 – 1.632<br/>nβ = 1.615 – 1.642 <br/>nγ = 1.632 – 1.665
| birefringence = δ = 0.021 – 0.033
| pleochroism = 
| 2V          = 
| dispersion  = weak r > v
| extinction  = 
| length fast/slow =
| fluorescence= Fluorescent, short UV=blue white mild peach, long UV=yellow
| absorption  =
| melt        = 
| fusibility  = 
| diagnostic  = 
| solubility  = 
| other       = 
| alteration  = 
| references  = <ref>{{Cite web|url=https://www.mineralienatlas.de/lexikon/index.php/MineralData?lang=de&mineral=Prehnite|title=Mineralienatlas - Fossilienatlas|website=www.mineralienatlas.de}}</ref><ref name=Webmin>{{Cite web|url=http://webmineral.com/data/Prehnite.shtml|title=Prehnite Mineral Data|website=webmineral.com}}</ref><ref name=Mindat>http://www.mindat.org/min-3277.html Mindat</ref><ref name=Manual>Hurlbut, Cornelius S.; Klein, Cornelis, 1985, ''Manual of Mineralogy'', 20th ed., {{ISBN|0-471-80580-7}}</ref><ref name=Handbook>http://rruff.geo.arizona.edu/doclib/hom/prehnite.pdf Handbook of Mineralogy</ref>
}}
'''Prehnite''' is an [[inosilicate]] of [[calcium]] and [[aluminium]] with the formula: Ca<sub>2</sub>Al(AlSi<sub>3</sub>O<sub>10</sub>)(OH)<sub>2</sub> with limited Fe<sup>3+</sup> substitutes for aluminium in the structure.<ref name="Der">{{cite book |url=https://books.google.com/books?id=5WEYTb9UAwQC&pg=PA271 |page=271 |title=Rock Forming Minerals: Layered Silicates Excluding Micas and Clay Minerals |volume=3B |author1=William Alexander Deer |author2=Robert Andrew Howie |author3=J. Zussman |publisher=Geological Society of London |year=1978|isbn=9781862392595 }}</ref> Prehnite crystallizes in the [[orthorhombic]] [[crystal]] system,<ref name="Der"/> and most often forms as stalactitic, [[botryoidal]], reniform or globular aggregates,<ref name="UsMus">{{cite book |url=https://books.google.com/books?id=BM3RAAAAMAAJ&pg=PA520 |page=520 |title=Report Upon the Condition and Progress of the U.S. National Museum During the Year Ending June 30, 1900 |series=[[United States National Museum]] |publisher=U.S. Government Printing Office |year=1902}}</ref> with only just the crests of small crystals showing any faces, which are almost always curved or composite. Very rarely will it form distinct, well-individualized crystals showing a square-like cross-section, including those found at the [[Jeffrey Mine]] in Asbestos, Quebec, [[Canada]]. Prehnite is brittle with an uneven fracture and a vitreous to pearly luster. Its [[Mohs scale of mineral hardness|hardness]] is 6.5, its [[specific gravity]] is 2.80–2.95 and its color varies from light green to yellow, but also colorless,<ref name="UsMus"/> blue, pink or white. In April 2000, rare orange prehnite was discovered in the Kalahari Manganese Fields, [[South Africa]]. Prehnite is mostly translucent, and rarely transparent.

Though not a [[zeolite]], prehnite is found associated with minerals such as [[datolite]], [[calcite]], [[apophyllite]], [[epidote]], [[stilbite]], [[laumontite]], and [[heulandite]] in veins and cavities of [[basalt]]ic rocks, sometimes in [[granite]]s, [[syenite]]s, or [[gneiss]]es. It is an indicator mineral of the [[Prehnite-pumpellyite facies|prehnite-pumpellyite metamorphic facies]]. 

It was first described in 1788 for an occurrence in the [[Karoo System|Karoo dolerites]] of [[Cradock, Eastern Cape|Cradock]], [[Eastern Cape Province]], [[South Africa]].<ref name=Mindat/> It was named for Colonel [[Hendrik Von Prehn]] (1733–1785), commander of the military forces of the [[Netherlands|Dutch]] colony at the [[Cape of Good Hope]] from 1768 to 1780.<ref name=Mindat/>

It is used as a gemstone.<ref>''Tables of Gemstone Identification'' By Roger Dedeyne, Ivo Quintens, p. 131</ref> 

Extensive deposits of gem-quality prehnite occur in the basalt tableland surrounding [[Wave Hill Station]] in the central [[Northern Territory]], of Australia.<ref>{{cite web|url=https://fossicking.nt.gov.au/declared-fossicking-areas/wave-hill|title=Wave Hill|department=History; Discoveries|date=2016|website=fossicking.nt.gov.au|access-date=2019-07-11}}</ref>

==Gallery==
<gallery widths="145px" heights="100px>
Image:prehnite-pf-0002.jpg|Emerald cut prehnite, 1.85&nbsp;cm × 1.42&nbsp;cm, 4.6 grams.
Image:Calcite-Prehnite-188139.jpg|Thin plate of pea-green prehnite on which have grown calcites
Image:Prehnite-273380.jpg|Water green color spheres of crystallized prehnite with minor calcite on basalt
Image:prehnite-pp-0134.jpg|Carved yellow prehnite pendant, 2.4&nbsp;cm × 1.8&nbsp;cm, 5.5 grams
Image:Prehnite-288989.jpg|Pastel-green rosettes of prehnite blades on matrix
Image:prehnite-ps-0107-DV00018.jpg|Prehnite nodule fragment, 11.0&nbsp;cm × 7.0&nbsp;cm, 338 grams.
Image:prehnite-ps-0128.jpg|Sliced prehnite fragment with calcite core, 9.0&nbsp;cm diameter.
Image:Prehnite-131722.jpg|A 2&nbsp;cm prehnite ball of top quality and color
</gallery>

==See also==
{{Commons category}}
*[[List of minerals]]
*[[List of minerals named after people]]

==References==
{{Reflist}}
[[Category:Aluminium minerals]]
[[Category:Calcium minerals]]
[[Category:Gemstones]]
[[Category:Inosilicates]]
[[Category:Minerals in space group 28]]
[[Category:Orthorhombic minerals]]
[[Category:Minerals described in 1788]]