Serandite

Serandite

Serandite 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 system Triclinic
Crystal class Pinacoidal (1)
(same H-M symbol)
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
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]

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]

Description

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]

History

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.[6] 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

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.[1]

References

  1. 1 2 3 4 5 6 "Sérandite" (PDF). Handbook of Mineralogy. Mineral Data Publishing. Retrieved July 11, 2012.
  2. 1 2 3 4 5 "Sérandite". Mindat. Retrieved July 11, 2012.
  3. ↑ "Serandite". Webmineral. Retrieved July 25, 2012.
  4. ↑ Hålenius, U., Hatert, F., Pasero, M., and Mills, S.J., IMA Commission on New Minerals, Nomenclature and Classification (CNMNC) Newsletter 28. Mineralogical Magazine 79(7), 1859–1864
  5. ↑ Manning, p. 357.
  6. ↑ Lacroix, p. 189.

Bibliography

Further reading

Media related to sérandite at Wikimedia Commons

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