Celadonite

{{Short description|Phyllosilicate mineral in the mica group}}

{{distinguish|Caledonite}}

{{Infobox mineral

| name = Celadonite

| boxbgcolor =#288436

| boxtextcolor = #fff

| image = Celadonite-Heulandite-Ca-pkn55b.jpg

| alt =

| caption = Green crystals of heulandite which owe their green colour to many tiny inclusions of celadonite

| category = Phyllosilicate minerals, mica group, celadonite subgroup

| formula = {{chem2|K(MgFe^{3+}◻)(Si4O10)(OH)2}}

| IMAsymbol=Cel{{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}}

| system = Monoclinic

| class = Spheroidal (2)
(same H-M symbol)

| symmetry = C2

| color =Blue-green to olive to applegreen

| cleavage =perfect on {001}

| tenacity =Fragile

| mohs =2

| luster =Waxy, dull, earthy

| diaphaneity =Translucent

| gravity =2.95 - 3.05

| density =2.95 - 3.05

| opticalprop =Biaxial (-)

| pleochroism =Visible

| 2V =5°- 8°

| impurities =Mn, Na, Ca

| other =25px Radioactive 9.11% (K)

| references = [https://www.mineralienatlas.de/lexikon/index.php/MineralData?mineral=Celadonite Mineralienatlas][http://www.mindat.org/show.php?id=926&ld=1&pho= Mindat w/ localities][http://webmineral.com/data/Celadonite.shtml Webmineral]

}}

Celadonite is a mica group mineral, a phyllosilicate of potassium, iron in both oxidation states, aluminium and hydroxide with formula {{chem2|K(MgFe^{3+}◻)(Si4O10)(OH)2}}.

It crystallizes in the monoclinic system and usually forms massive aggregates of prismatic crystallites or, more commonly, in dull clay masses. It is soft with a Mohs hardness of 2 and a specific gravity of 3. It forms vesicle fillings and linings in altered basaltic lavas. Early research suggests this mineral has ties to weakly metamorphosed plutonic rocks during formation, and is also found with montmorillonite clays or zeolite crystals.{{Cite journal |last1=Wise |first1=W.S. |last2=Euster |first2=H.P |date=August 1964 |title=Celadonite: synthesis, thermal stability and occurrence. American Mineralogist, 1974 (7-8): 1031-1083 |url=https://pubs.geoscienceworld.org/msa/ammin/article/49/7-8/1031/539937/Celadonite-synthesis-thermal-stability-and |journal=American Mineralogist|volume=49 |issue=7–8 |pages=1031–1083 }} Association with zeolites may indicate these minerals favor the same underlying conditions of crystal growth.

It was first described in 1847 on Monte Baldo, near Verona, Italy. The name is from the French celadon, for sea-green. It is one of two minerals, along with glauconite, used in making the pigment known as green earth,{{Cite journal |last1=Hradil |first1=David |last2=Grygar |first2=Tomáš |last3=Hrušková |first3=Michaela |last4=Bezdička |first4=Petr |last5=Lang |first5=Kamil |last6=Schneeweiss |first6=Oldřich |last7=Chvátal |first7=Marek |date=2004-12-01 |title=Green Earth Pigment from the Kadaň Region, Czech Republic: Use of Rare Fe-rich Smectite |url=https://doi.org/10.1346/CCMN.2004.0520612 |journal=Clays and Clay Minerals |language=en |volume=52 |issue=6 |pages=767–778 |doi=10.1346/CCMN.2004.0520612 |bibcode=2004CCM....52..767H |s2cid=95885389 |issn=1552-8367|url-access=subscription }} which was an important pigment for the decoration of Joseon buildings (so much so that the only site which produces celadonite in South Korea is a designated natural monument).{{Cite web |title=포항 뇌성산 뇌록산지 (浦項 磊城山 磊綠産地) Pohang Noeseongsan Noeroksanji |url=https://www.heritage.go.kr/heri/cul/culSelectDetail.do?pageNo=1_1_2_0&VdkVgwKey=16,05470000,37 |access-date=2025-02-16 |website=National Heritage (www.heritage.go.kr/) |language=ko}}

Common impurities are manganese, calcium and sodium (previously known as natrium).