- Népouite
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Népouite 
Népouite from Népoui Mine, North Province, New Caledonia, New Caledonia Specimen size 21 cm.General Category Phyllosilicate Chemical formula Ni3(Si2O5)(OH)4 Strunz classification 9.ED.15 Dana classification 71.1.2b.3 Identification Colour bright green (typical of nickel bearing silicates) to yellowish or brownish green, depending on nickel content Crystal habit generally massive, also fibrous and microscopic pseudohexagonal platy crystals Crystal system Orthorhombic Pyramidal H-M Symbol mm2 Cleavage perfect on {001} Mohs scale hardness 2 to 2½ Luster earthy to waxy, also pearly Streak greenish white Diaphaneity semitranslucent Specific gravity 3.18 to 3.24 (measured) Optical properties Biaxial (-) Refractive index nα = 1.600 - 1.630 nγ = 1.635 - 1.650 Birefringence 0.035 Pleochroism Weak. X = green to yellow green Z = yellow-green References [1][2][3] Népouite is a rare nickel silicate mineral which has the apple green colour typical of such compounds. It was named by E Glasser in 1907 after the place where it was first described (the type locality), the Népoui Mine, Népoui, Nouméa Commune, Northern Province, New Caledonia. The ideal formula is Ni3(Si2O5)(OH)4, but most specimens contain some magnesium, and (Ni,Mg)3(Si2O5)(OH)4 is more realistic. There is a similar mineral called lizardite in which all the nickel is replaced by magnesium, formula Mg3(Si2O5)(OH)4.[4] These two minerals form a series, that is to say intermediate compositions are possible, with varying proportions of nickel to magnesium.[5]
Pecoraite is another rare mineral with the same chemical formula as népouite, but a different structure; such minerals are said 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.[6]
Garnierite is a green nickel ore that formed as a result of weathering of ultramafic rocks, and that occurs in many nickel deposits worldwide. It is a mixture of various nickel and magnesium phyllosilicates (sheet silicates), 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 has been found in Australia, Austria, the Czech Republic, the Democratic Republic of Congo, Germany, Greece, Italy, Japan, Morocco,[7] Poland, Russia, South Africa and the USA.
Structure
Space Group Ccm21. Unit Cell: a = 5.31 Å, b = 9.19 Å, c = 14.50 Å
X-Ray Powder Diffraction d spacing 7.31 4.55 3.63 2.89 2.50 2.31 2.20 1.53 relative intensity 10 5 9 6 7 4 4 6 References
- ^ http://rruff.geo.arizona.edu/doclib/hom/nepouite.pdf Handbook of Mineralogy
- ^ http://www.mindat.org/min-2882.html Mindat.org
- ^ http://www.webmineral.com/data/Nepouite.shtml Webmineral data
- ^ http://www.mindat.org/min-8771.html
- ^ American Mineralogist (1975): 60: 863-871
- ^ Dana’s New Mineralogy, Eighth Edition, 1997, Gaines et al., Wiley.
- ^ Mineralogical Record 38-5, page 384
Serpentine group Clay mineral group Chlorite1 · Dickite · Halloysite · Illite · Ilmenite · Kaolinite · Montmorillonite · Nacrite · Nontronite · Palygorskite · Saponite · Sepiolite · Serpentine1 · TalcMica group Chlorite group 1. Serpentine and Chlorite are sometimes considered clay mineralsCategories:- Serpentine group
- Nickel minerals
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