Noelbensonite

noelbensonite

tokyoite

demagistrisite

namansilite

Images

Formula: BaMn3+2Si2O7(OH)2.H2O
Sorosilicate (Si2O7 groups), lawsonite group, barium- and manganese- bearing mineral
Crystal System: Orthorhombic
Specific gravity: 3.87 calculated
Hardness: 4
Streak: Yellow-brown
Colour: Dark brown
Environments

Metamorphic environments

Localities

At the type locality, Woods Mine, Inglis County, New South Wales, Australia, noelbensonite has been observed in the rhodonite deposit as a replacement of sodium-manganese amphibole or namansilite and serandite, and as the main or sole constituent of tiny veinlets 0.05 to 0.25 mm thick. Where such veinlets cut sodium-manganese amphibole or namansilite, replacement by noelbensonite spreads from the vein into the mineral, but volumetrically larger quantities of replacement noelbensonite occur as patches disseminated through the rock, sometimes up to a millimetre across.
The noelbensonite is clearly of late-stage origin, following the metamorphic maximum. Where occurring as a replacement, the noelbensonite occurs as dense mosaics of anhedral or somewhat elongate blocky grains from a few microns to (rarely) about 100 microns in length. In the veinlets it occurs both as similar but mostly finer-grained aggregates, and sometimes as finely foliated sheaves up to 100 microns long. Some veinlets have a discontinuous inner filling of quartz, K-feldspar and fluorapatite. In a very few places, euhedral noelbensonite is found in recrystallised patches at the edges of veinlets with quartz, barium-bearing K-feldspar and baryte (MM 60.369-374).
Other associated minerals include namansilite and pectolite (Mindat).
Noelbensonite from the Woods Mine - Image

At the Cerchiara Mine, Borghetto di Vara, La Spezia Province, Liguria, Italy, the ore consists of rhythmic interlaying of braunite-bearing metasediments 5 to 15 cm thick, and hematite-rich cherts. Demagistrisite occurs in association with cerchiaraite-(Mn), namansilite, noelbensonite, orientite, richterite, ruizite and saponite in matrix consisting of braunite, calcite, cryptomelane, orthoclase and quartz (CM 59.1.91–105).
Noelbensonite from the Cerchiara Mine - Image

At the Postmasburg manganese field, Northern Cape, South Africa, samples of manganese-rich rock containing tokyoite in association with noelbensonite were retrieved from a drill core. The samples consist of fine-grained braunite, hematite and hausmannite. Within this material abundant vugs are observed that are filled with witherite, baryte and barytocalcite. In addition, arsenic-rich tokyoite, tokyoite and noelbensonite occur in the centre of the vugs, in fine aggregates 0.1 to 1 mm in size. The outer walls of the vugs are lined with microcrystalline K-feldspar, witherite and/or serandite (CM 53.981–990).

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