népouite

{{Short description|Nickel ore from the serpentine family (phyllosilicate)}}

{{Infobox mineral

| name = Népouite

| category = Phyllosilicates
Kaolinite-serpentine group

| boxwidth =

| image = Népouite MHNT.MIN.2005.0.63.jpg

| imagesize = 260px

| caption = Népouite from the Népoui Mine, North Province, New Caledonia. Specimen size: 21 cm.

| formula = {{chem2|Ni3(Si2O5)(OH)4}}

| IMAsymbol = Npo{{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 |s2cid=235729616 |doi-access=free}}

| molweight =

| strunz = 9.ED.15

| dana = 71.1.2b.3

| system = Orthorhombic

| class = pyramidal (mm2)
(same H-M symbol)

| symmetry = Ccm2₁ (no. 36)

| color = bright green (typical of nickel bearing silicates) to yellowish or brownish green, depending on nickel content

| habit = generally massive, also fibrous and microscopic pseudohexagonal platy crystals

| cleavage = perfect on {001}

| mohs = 2 to {{frac|2|1|2}}

| luster = earthy to waxy, also pearly

| streak = greenish white

| diaphaneity = semitranslucent

| gravity = 3.18 to 3.24 (measured)

| density =

| opticalprop = biaxial (−)

| refractive = n_α = 1.600 – 1.630 n_γ = 1.635 – 1.650

| birefringence = 0.035

| pleochroism = weak. X = green to yellow green Z = yellow-green

| 2V =

| dispersion =

| references = http://rruff.geo.arizona.edu/doclib/hom/nepouite.pdf Handbook of Mineralogyhttp://www.mindat.org/min-2882.html Mindat.orghttp://www.webmineral.com/data/Nepouite.shtml Webmineral data

}}

Népouite is a rare nickel silicate mineral which has the apple green color typical of such compounds. It was named by the French mining engineer Edouard Glasser in 1907 after the place where it was first described (the type locality), the Népoui Mine, {{ill|Népoui|fr}}, Poya Commune, North Province, New Caledonia.{{Cite web |title=Note sur une espèce minérale nouvelle, la népouite, silicate hydraté de nickel et de magnésie. Bulletin de Minéralogie. Année 1907, 30 (1), pp. 17–28. – Sur le site de Persée |trans-title=Note on a new mineral species, népouite, hydrated silicate of nickel and magnesia. Bulletin de Minéralogie. Year 1907, 30 (1), pp. 17–28. – On the Persée website |author=M. E. Glaser |work=persee.fr |date=1907 |access-date=28 November 2022 |url= https://www.persee.fr/doc/bulmi_0366-3248_1907_num_30_1_2797 |language=fr}} The ideal formula is {{chem2|Ni3(Si2O5)(OH)4}}, but most specimens contain some magnesium, and {{chem2|(Ni,Mg)3(Si2O5)(OH)4}} is more realistic. There is a similar mineral called lizardite (named after the Lizard Complex in Cornwall, England) in which all of the nickel is replaced by magnesium, formula {{chem2|Mg3(Si2O5)(OH)4}}.{{Cite web|url=http://www.mindat.org/min-8771.html|title = Lizardite-Népouite Series}} These two minerals form a series; intermediate compositions are possible, with varying proportions of nickel to magnesium.American Mineralogist (1975): 60: 863–871

Pecoraite is another rare mineral with the same chemical formula as népouite, but a different structure; such minerals are said{{by who|date=January 2025}} to be dimorphs of each other, in the same way as graphite is a dimorph of diamond. Népouite, lizardite and pecoraite are all members of the kaolinite-serpentine group.Dana’s New Mineralogy, Eighth Edition, 1997, Gaines et al., Wiley.

Garnierite is a green nickel ore that formed as a result of weathering of ultramafic rocks, and that occurs in many{{quantify|date=January 2025}} nickel deposits{{examples|date=January 2025}} worldwide. It is a mixture of various nickel and magnesium phyllosilicates, including népouite. Associated minerals include calcite, chlorite, goethite, halloysite, nontronite, pimelite, quartz, sepiolite, serpentine, talc and willemseite.

As well as the type locality in New Caledonia, it is present in Australia, Austria, the Czech Republic, the Democratic Republic of Congo, Germany, Greece, Italy, Japan, Morocco,Mineralogical Record 38-5, page 384 Poland, Russia, South Africa and the United States.