Sérandite

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Sérandite
Serandite-d05-45a.jpg
Sérandite from Mont Saint-Hilaire, Quebec, Canada
General
Category Inosilicates
Formula
(repeating unit)
Na(Mn2+,Ca)2Si3O8(OH).
Strunz classification 9.DG.05
Dana classification 65.2.1.5
Crystal symmetry Pinacoidal
H-M symbol: 1
Space group: P1
Unit cell a = 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
Crystal system Triclinic
Twinning Around [010] composition plane {100}, less commonly contact twin on {110}
Cleavage Perfect on {001} and {100}
Fracture Irregular, uneven
Tenacity Brittle
Mohs scale hardness 5 to 5.5
Luster Vitreous to greasy; fibrous aggregates are dull to silky[1]
Streak White
Diaphaneity Transparent, Translucent
Density 3.34 g/cm3 (measured)
Optical properties Biaxial (+)
Refractive index nα = 1.668
nβ = 1.671
nγ = 1.703
Birefringence δ = 0.035
2V angle 39°
Dispersion r < v moderate
References [2]

Sérandite, also 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. Sérandite is generally red, brown, black or colorless.

Description[edit]

Sérandite 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.[4]

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]

History[edit]

Sérandite 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.[5] He named it sérandite in honor of J.M. Sérand, a mineral collector who helped in the collection of the mineral.[2]

Occurrence and distribution[edit]

Sérandite 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, sérandite 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, sérandite occurs in a manganese rich deposit associated with volcanic rocks and terrigenous (non-marine) sediments which has been altered by contact metamorphism.[1]

Sérandite has been found in association with aegirine, analcime, arfvedsonite, astrophyllite, eudialyte, fluorite, leucophanite, mangan-neptunite, microcline, nepheline, sodalite, and villiaumite.[1]

References[edit]

  1. ^ a b c d e f "Sérandite" (PDF). Handbook of Mineralogy. Mineral Data Publishing. Retrieved July 11, 2012. 
  2. ^ a b c d e "Sérandite". Mindat. Retrieved July 11, 2012. 
  3. ^ "Serandite". Webmineral. Retrieved July 25, 2012. 
  4. ^ Manning, p. 357.
  5. ^ Lacroix, p. 189.

Bibliography[edit]

Further reading[edit]

External links[edit]

Media related to sérandite at Wikimedia Commons