birnessite

manganese

Serandite

Formula: NaMn2+2Si3O8(OH)
Inosilicate (chain silicate), wollastonite group, forms a series with pectolite
Specific gravity: 3.34
Hardness: 5 to 5½
Streak: White
Colour: Characteristic deep orange, also pink, red, brown and yellow. Some crystals are black due to surface oxidation or alteration to manganese oxides (R&M 94.4.350).
Solubility:
Environments:

Plutonic igneous environments
Pegmatites most common
Metamorphic environments

Serandite is a silicate of sodium and manganese; it occurs in alkaline rocks and syenite pegmatites (Dana, R&M 94.4.352), associated with arfvedsonite, astrophyllite, eudialyte, fluorite, leucophanite, manganoneptunite, microcline, nepheline and sodalite (Mindat).
Serandite alters to birnessite. Pseudomorphs of elpidite, nenadkevichite, birnessite and rhodochrosite are known (Dana).

At Mount Goonerineggeringgi, Queensland, Australia, serandite occurs in a phonolite dike (Dana).

At the Poudrette quarry, Mont Saint-Hilaire, Montérégie, Québec, Canada, serandite occurs in pegmatites cutting syenite and nepheline syenite, associated with analcime, aegirine, natrolite, microcline and manganoneptunite. It is also found with leifite intergrown with eirikite, and occasionally serandite has been found in sodalite xenoliths (R&M 94.4.352-354, HOM). Pseudomorphs after serandite are common here, with the replacing minerals including elpidite, natrolite, birnessite, ranciéite, rhodochrosite and siderite (R&M 94.4.352-354).

At the type locality, Rouma Island, Los Archipelago, Guinea, serandite occurs in a nepheline syenite pegmatite (Mindat), associated with arfvedsonite, aegirine, analcime, astrophyllite, eudialyte, catapleiite, sodalite, nepheline, fluorite, eudialyte, leucophanite and villiaumite (AM 16.344, R&M 94.4.352, Mindat, HOM).

At the Shiromaru mine, Nishitama district, Tokyo, Japan, serandite occurs with banalsite (Dana).

In the area of the Langesundsfjorden, Bamble, Telemark fylke, Norway, serandite occurs in pegmatites in nepheline syenite and larvikite (R&M 94.4.355).

At the Sagåsen Quarry, Mørje, Porsgrunn, Telemark, Norway, serandite occurs in analcime (R&M 94.4.355).

At the Tumannoe copper deposit, Pushchino, Kamchatka Krai, Russiain, serandite occurs in a contact metamorphosed manganese deposit (HOM).

At the Shkatulka pegmatite in the Umbozero mine, Alluaiv Mountain, Lovozero Massif, Murmansk Oblast, Russia, serandite occurs embedded in ussingite (R&M 94.4.350).

At the Palitra pegmatite, Kedykverpakhk Mountain, Lovozero Massif, Murmansk Oblast, Russia, large masses of natrosilite enclose serandite. Serandite crystals have also been found on ussingite associated with lomonosovite, and as replacements of manaksite (R&M 94.4.354). It is associated with ussingite and villiaumite included in natrosilite, and it also occurs as pseudomorphs after manaksite, associated with aegirine (MinRec 36.5.410-411).

In the Wessels Mine, Hotazel, Kalahari manganese field, Northern Cape, South Africa, serandite occurs in deposits of manganese and iron oxides filling cavities between sugilite crystals (but only visible in thin sections) (R&M 94.4.355-356).

At Point of Rocks, Springer, Colfax county, New Mexico, USA, serandite is found in vugs in phonolite (HOM).

Common impurities: Al,Fe,Mg,K,H2O

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