| Serandite | |
|---|---|
 Serandite fromMont Saint-Hilaire, Quebec, Canada | |
| General | |
| Category | Inosilicates |
| Formula | Na(Mn2+,Ca)2Si3O8(OH) |
| IMA symbol | Srd[1] |
| Strunz classification | 9.DG.05 |
| Dana classification | 65.2.1.5 |
| Crystal system | Triclinic |
| Crystal class | Pinacoidal (1) (sameH-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 | |
| Colour | salmon pink to orange |
| 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[2] |
| 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 | [3] |
Serandite[4] is amineral with formula Na(Mn2+,Ca)2Si3O8(OH). The mineral was discovered inGuinea in 1931 and named for J. M. Sérand. Serandite is generally red, brown, black or colorless. The correct name lacks an accent.[5]
Serandite is transparent to translucent and is normally salmon-pink, light pink, rose-red, orange, brown, black, or colorless; inthin section, it is colorless.[2] Octahedrally bondedMn(II) is the primary contributor to the mineral's pink colors.[6]
Crystals of the mineral can be prismatic toacicular and elongated along [010], bladed, blocky, or tabular and flattened on {100}, occur as a radiating aggregate, or have massivehabit.[2] Sérandite is a member of the wollastonite group and is the manganese analogue ofpectolite.[3] It is sometimes used as a gemstone.[7]
Serandite was discovered on Rouma Island, part of theLos Islands in Guinea.[3] The mineral was described by À. Lacroix in the journalComptes rendus hebdomadaires des séances de l'Académie des Sciences.[8] He named itsérandite in honor of J.M. Sérand, a mineral collector who helped in the collection of the mineral.[3]
Serandite has been found in Australia, Brazil, Canada, Guinea, Italy, Japan, Namibia, Norway, Russia, South Africa, and the United States.[3] Thetype material is held at theNational Museum of Natural History in Washington, D.C.[2]
AtMont Saint-Hilaire, Quebec, serandite occurs in sodalitexenoliths andpegmatites cuttingsyenites within an intrusivealkalicgabbro-syenite complex. In Pointof Rocks, New Mexico, it occurs invugs inphonolite. At the Tumannoe deposit in Russia, serandite occurs in a manganese rich deposit associated withvolcanic rocks andterrigenous (non-marine)sediments which has been altered bycontact metamorphism.[2]
Serandite has been found in association withaegirine,analcime,arfvedsonite,astrophyllite,eudialyte,fluorite,leucophanite, mangan-neptunite,microcline,nepheline,sodalite, andvilliaumite.[2]
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