View source for Chemistry:Chrysoprase

{{Short description|Gemstone variety of chalcedony}}
{{Infobox mineral
| name        = Chrysoprase
| category    = 
| boxwidth    =
| boxbgcolor  = #5AFFAB
| boxtextcolor = black
| image       = Chryzopras Polsko.jpg
| alt         = 
| caption     = Chrysoprase (Poland) 
| formula     = SiO<sub>2</sub>
| molweight   = 
| symmetry    = 
| class       = 
| color       = Olive to applegreen
| habit       = Microcrystalline aggregates
| system      = Trigonal
| twinning    = 
| cleavage    = None
| fracture    = Conchoidal, granular
| tenacity=Brittle
| mohs        = 6.0–7.0
| luster      = Greasy, waxy
| polish      = 
| refractive  = 
| opticalprop = 
| birefringence = 0.004–0.009
| pleochroism = 
| dispersion  = None
| streak      = 
| gravity     = 2.651–2.91
| melt        = 
| fusibility  = 
| diagnostic  = 
| solubility  = 
| diaphaneity = Nearly opaque to nearly transparent 
| fluorescence = None
| other       = 
| references = <ref>[http://www.mindat.org/min-952.html Mindat.org]</ref>
}}
'''Chrysoprase''', '''chrysophrase''' or '''chrysoprasus''' is a [[Earth:Gemstone|gemstone]] variety of [[Chemistry:Chalcedony|chalcedony]] (a [[Earth:Cryptocrystalline|cryptocrystalline]] form of [[Chemistry:Silica|silica]]) that contains small quantities of [[Chemistry:Nickel|nickel]]. Its color is normally apple-green, but varies from [[Chemistry:Turquoise|turquoise]]-like cyan to deep green. The darker varieties of chrysoprase are also referred to as '''prase'''. (However, the term prase is also used to describe [[Chemistry:Chlorite group|chlorite]]-included quartz, and to a certain extent is a color-descriptor, rather than a rigorously defined mineral variety.)

Chrysoprase is cryptocrystalline, which means that it is composed of crystals so fine that they cannot be seen as distinct particles under normal magnification. This sets it apart from rock crystal, [[Chemistry:Amethyst|amethyst]], [[Chemistry:Quartz#Citrine|citrine]], and the other varieties of crystalline quartz. Other members of the cryptocrystalline silica family include [[Chemistry:Agate|agate]], [[Chemistry:Carnelian|carnelian]], and [[Chemistry:Onyx|onyx]]. Unlike many non-transparent silica minerals, it is the color of chrysoprase, rather than any pattern of markings, that makes it desirable. The word chrysoprase comes from the Greek {{wikt-lang|grc|χρυσός}} ''chrysos'' meaning 'gold' and {{wikt-lang|grc|πράσινον}} ''prasinon'', meaning 'green'.

Unlike [[Chemistry:Emerald|emerald]] which owes its green color to the presence of [[Chemistry:Chromium|chromium]], the color of chrysoprase is due to trace amounts of [[Chemistry:Nickel|nickel]] compounds in the form of very small inclusions. The nickel reportedly occurs as different silicates, like [[Chemistry:Kerolite|kerolite]] or [[Chemistry:Pimelite|pimelite]] (not NiO mineral, [[Chemistry:Bunsenite|bunsenite]], as was reported before). Chrysoprase results from the deep weathering or [[Earth:Laterite|lateritization]] of nickeliferous [[Earth:Serpentinite|serpentinite]]s or other [[Chemistry:Ultramafic rock|ultramafic]] [[Earth:Ophiolite|ophiolite]] rocks. In the Australian deposits, chrysoprase occurs as veins and nodules with brown [[Chemistry:Goethite|goethite]] and other [[Chemistry:Iron oxide|iron oxide]]s in the [[Chemistry:Magnesite|magnesite]]-rich [[Earth:Saprolite|saprolite]] below an iron and silica cap.

As with all forms of [[Chemistry:Chalcedony|chalcedony]], chrysoprase has a hardness of 6 to 7 on the [[Physics:Mohs scale of mineral hardness|Mohs hardness scale]] and a conchoidal fracture like [[Earth:Flint|flint]].

The best known sources of chrysoprase are Indonesia, Queensland, Western Australia, Haneti Tanzania, {{wipe|Germany}}, {{wipe|Poland}}, {{wipe|Russia}}, Arizona, {{wipe|California}}, and {{wipe|Brazil}}. Deposits in central Tanzania have been in constant production since 1986. The chrysoprase and nickel silicate ore deposit in Szklary, Lower Silesia, {{wipe|Poland}}, was probably the biggest European chrysoprase occurrence and possibly also the biggest in the world.{{Citation needed|date=August 2011}}

A very similar mineral to chrysoprase is [[Chemistry:Chrome chalcedony|chrome chalcedony]], in which the color is provided by [[Chemistry:Chromium|chromium]] rather than nickel.

==See also==
* [[Chemistry:Chalcedony|Chalcedony]]

==References==
{{reflist}}
* [https://www.gemsociety.org/article/chrysoprase-gem-information/ Gemsociety.org]
* [https://www.gemdat.org/gem-952.html Gemdat.org]

== External links ==
{{EB1911 poster|Chrysoprase}}

{{Silica minerals}}
{{Gemstones}}

[[Category:Chalcedony]]
[[Category:Quartz gemstones]]

{{Sourceattribution|Chrysoprase}}