Serandite

Serandite[3] is a mineral with formula Na(Mn2+,Ca)2Si3O8(OH). The mineral was discovered in Guinea in 1931 and named for J. M. Sérand. Serandite is generally red, brown, black or colorless. The correct name lacks an accent.[4]

Serandite
Serandite-Aegirine-20264.jpg
Serandite from Mont Saint-Hilaire, Quebec, Canada
General
CategoryInosilicates
Formula
(repeating unit)		Na(Mn2+,Ca)2Si3O8(OH)
Strunz classification9.DG.05
Dana classification65.2.1.5
Crystal systemTriclinic
Crystal classPinacoidal (1)
(same H-M symbol)
Space groupP1
Unit cella = 7.683(1) Å, b = 6.889(1) Å
c = 6.747(1) Å, α = 90.53(5)°
β = 94.12(2)°, γ = 102.75(2)°
Z = 2
Identification
Coloursalmon pink to orange
TwinningAround [010] composition plane {100}, less commonly contact twin on {110}
CleavagePerfect on {001} and {100}
FractureIrregular, uneven
TenacityBrittle
Mohs scale hardness5 to 5.5
LusterVitreous to greasy; fibrous aggregates are dull to silky[1]
StreakWhite
DiaphaneityTransparent, Translucent
Density3.34 g/cm3 (measured)
Optical propertiesBiaxial (+)
Refractive indexnα = 1.668
nβ = 1.671
nγ = 1.703
Birefringenceδ = 0.035
2V angle39°
Dispersionr < v moderate
References[2]

DescriptionEdit

Serandite is transparent to translucent and is normally salmon-pink, light pink, rose-red, orange, brown, black, or colorless; in thin section, it is colorless.[1] Octahedrally bonded Mn(II) is the primary contributor to the mineral's pink colors.[5]

Crystals of the mineral can be prismatic to acicular and elongated along [010], bladed, blocky, or tabular and flattened on {100}, occur as a radiating aggregate, or have massive habit.[1] Sérandite is a member of the wollastonite group and is the manganese analogue of pectolite.[2] It is sometimes used as a gemstone.[6]

HistoryEdit

Serandite was discovered on Rouma Island, part of the Los Islands in Guinea.[2] The mineral was described by À. Lacroix in the journal Comptes rendus hebdomadaires des séances de l'Académie des Sciences.[7] He named it sérandite in honor of J.M. Sérand, a mineral collector who helped in the collection of the mineral.[2]

Occurrence and distributionEdit

Serandite has been found in Australia, Brazil, Canada, Guinea, Italy, Japan, Namibia, Norway, Russia, South Africa, and the United States.[2] The type material is held at the National Museum of Natural History in Washington, D.C.[1]

At Mont Saint-Hilaire, Quebec, serandite occurs in sodalite xenoliths and pegmatites cutting syenites within an intrusive alkalic gabbro-syenite complex. In Point of Rocks, New Mexico, it occurs in vugs in phonolite. At the Tumannoe deposit in Russia, serandite occurs in a manganese rich deposit associated with volcanic rocks and terrigenous (non-marine) sediments which has been altered by contact metamorphism.[1]

Serandite has been found in association with aegirine, analcime, arfvedsonite, astrophyllite, eudialyte, fluorite, leucophanite, mangan-neptunite, microcline, nepheline, sodalite, and villiaumite. 


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 Metasyntactic variable, which is released under the 
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