Nambulite

Formula: LiMn²⁺₄Si₅O₁₄(OH)
Inosilicate (chain silicate), forms a series with natronambulite
Specific gravity: 3.53
Hardness: 6½
Streak: Pale yellow
Colour: Pale tan to orange-brown to deep red
Common impurities: Ti,Al,Fe,Mg,Ca,K,H₂O,C,P
Environments

Hydrothermal environments

Localities

At Obernberger Tribulaun, Obernberg am Brenner, Innsbruck-Land District, Tyrol, Austria, the first discovery of nambulite in Austria was made in 2018. The deposit consists of small lenses containing a variety of manganese-bearing minerals in quartzitic metamorphosed radiolarite. The nambulite occurs as irregular, small, orange-yellow masses up to several centimeters infilling fractures (R&M 95.6.532).

At the Figuerinha Mine, Urucum massif, Corumbá, Mato Grosso do Sul, Brazil, bright orange fibrous nambulite to 1 cm in radially oriented clusters occurs. It forms in thin veinlets to 30 mm associated with K-feldspar, baryte and calcite. These are hosted in massive braunite-rich ore, originally formed by primary sedimentary processes but modified by later metamorphism (http://www.mme.gov.na/files/publications/759_Schneider_Nambulite.pdf, R&M 95.6.532-533).

At the Cerchiara Mine, Borghetto di Vara, La Spezia Province, Liguria, Italy, small, pale pink to off-white nambulite crystals occur. Braunite and hematite are the two main ore minerals (R&M 95.6.532).

At the type locality, the Funakozawa mine, Ono, Hirono-cho, Kunohe-gun, Iwate Prefecture, Japan, nambulite occurs in veinlets cutting braunite ore in chert. Associated minerals include braunite, albite, neotocite and rhodochrosite (HOM).

At the Tunakozawa mine, Kitakami Mountains, Iwate Prefecture, Japan, nambulite occurs in veinlets up to 5 cm thick that cut braunite ore in chert. Associated minerals include albite, neotocite and rhodochrosite (AM 58.1112).

At the Kombat Mine, Kombat, Grootfontein, Otjozondjupa Region, Namibia, a hydrothermal vein system cuts through the layering of manganese ore bodies. The nambulite-bearing veins are up to 10 cm thick and contain prismatic, light red crystals up to 3x4x2 mm, as well as small, fibrous, pink crystals. Matrix specimens consist primarily of gypsum with scattered nambulite crystals embedded therein. On the contact surfaces with the nambulite, the gypsum is replaced by acicular brown brushite, and inclusions of cahnite are common in the gypsum. Rare, small, yellow-brown prismatic crystals of kentrolite are present as are baryte and calcite. The nambulite crystals are the finest known and vary in size from a few millimeters to 3 cm. They are typically vibrant red and translucent to transparent (R&M 95.6.530-534, http://www.mme.gov.na/files/publications/759_Schneider_Nambulite.pdf).

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