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
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).
Back to Minerals