| Serandite | |
| Category: | Inosilicates |
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| Formula: | Na(Mn2+,Ca)2Si3O8(OH) |
| Imasymbol: | Srd[1] |
| Strunz: | 9.DG.05 |
| Dana: | 65.2.1.5 |
| System: | Triclinic |
| Class: | Pinacoidal (same H-M symbol) |
| Symmetry: | P |
| 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 |
| Twinning: | Around [010] composition plane, less commonly contact twin on |
| Cleavage: | Perfect on and |
| Fracture: | Irregular, uneven |
| Tenacity: | Brittle |
| Mohs: | 5 to 5.5 |
| Luster: | Vitreous to greasy; fibrous aggregates are dull to silky[2] |
| Refractive: | nα = 1.668 nβ = 1.671 nγ = 1.703 |
| Opticalprop: | Biaxial (+) |
| Birefringence: | δ = 0.035 |
| 2V: | 39° |
| Dispersion: | r < v moderate |
| Streak: | White |
| Density: | 3.34 g/cm3 (measured) |
| Diaphaneity: | Transparent, Translucent |
| References: | [3] |
| Colour: | salmon pink to orange |
Serandite[4] 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.[5]
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.[2] Octahedrally bonded Mn(II) is the primary contributor to the mineral's pink colors.[6]
Crystals of the mineral can be prismatic to acicular and elongated along [010], bladed, blocky, or tabular and flattened on, occur as a radiating aggregate, or have massive habit.[2] Sérandite is a member of the wollastonite group and is the manganese analogue of pectolite.[3] It is sometimes used as a gemstone.[7]
Serandite was discovered on Rouma Island, part of the Los Islands in Guinea.[3] The mineral was described by À. Lacroix in the journal Comptes rendus hebdomadaires des séances de l'Académie des Sciences.[8] He named it sérandite 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] The type material is held at the National Museum of Natural History in Washington, D.C.[2]
At Mont Saint-Hilaire, Quebec, serandite occurs in sodalite xenoliths and pegmatites cutting syenites within an intrusive alkalic gabbro-syenite complex. In Pointof 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.[2]
Serandite has been found in association with aegirine, analcime, arfvedsonite, astrophyllite, eudialyte, fluorite, leucophanite, mangan-neptunite, microcline, nepheline, sodalite, and villiaumite.[2]