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Formula: (Na,Ca,K,Ba,Sr)1-x(Mn,Mg,Al)6O12.3-4H2O
Multiple oxide, barium-,
strontium- and manganese-
bearing mineral
Crystal System: Monoclinic
Specific gravity: 3.67 measured, 3.65 calculated
Hardness: 1½
Streak: Brown, black, lead-grey
Colour: Purplish grey, brown to black, brown in transmitted light
Solubility: Soluble in hydrochloric acid with evolution of Cl2
Common impurities: Ba,K,Na
Environments:
Pegmatites
Hydrothermal environments
Todorokite occurs as aggregates of minute,lath-like crystals. Although it is a common product of oxidation and leaching of
primary manganese carbonate and silicate minerals, its major occurrence is as
the dominant Mn4+ phase of deep sea ferromanganese nodules
(Dana). Associated minerals include pyrolusite,
cryptomelane, romanèchite,
manganite, rhodochrosite,
quartz, opal,
albite, baryte,
birnessite, calcite,
chabazite, chalcophanite,
colemanite, fluorapatite,
gypsum, hollandite,
lévyne, magnesite,
microcline, muscovite,
nontronite and stilbite
(HOM, Mindat).
It is also found as a late stage coating in granite pegmatites
(Mindat).
Localities
At the Willy Wally Gully, Merriwa, Brisbane county, New South Wales, Australia, the paragenetic sequence was
saponite → lévyne-(Ca)
→ offretite → chabazite-(Ca)
→ phillipsite-Ca → aragonite
→ calcite → todorokite (AJM 16.2.80). Todorokite is rare
and occurs either directly deposited on saponite vesicle linings when other minerals are
absent, or adhering to the surface of chabazite-(Ca) or
lévyne-(Ca)-offretite crystals
(AJM 16.2.85).
At Hüttenberg, Sankt Veit an der Glan District, Carinthia, Austria, fragile, soft nodular masses of todorokite about 5 cm
in diameter occur with a few thin intercalated layers of pyrolusite. Aggrgates of soft
manganese oxides occur at Hüttenberg together with hard, black coatings of
secondary manganese minerals that probably include
cryptomelane and hollandite
(AM 45.1169-1170).
At Saúde, Serra de Jacobina, and Urandi, both at Bahia, Brazil, todorokite has been identified as a rare constituent of
manganese oxide deposits which are largely the result of supergene
enrichment of metamorphic country rock containing spessartine and other manganese minerals
(AM 45.1171).
At the Charco Redondo mine, Santa Rita, Granma Province, Cuba, todorokite occurs with
pyrolusite, cryptomelane,
manganite and psilomelane
(Dana).
At the Montenegro mine, Sierra Maestra Mountains, Santiago de Cuba Province, Cuba, todorokite is confined to the contact
between the massive Charco Redondo limestone and underlying volcanic
tuff. Unlike most manganese deposits, these seem to be
secondary in nature. The todorokite appears to be a fissure or
breccia filling of hypogene
origin
(AM 45.802-807).
A museum specimen from Romanèche-Thorens, La Chapelle-de-Guinchay, Mâcon, Saône-et-Loire, Bourgogne-Franche-Comté, France, showed
a hard black crust of psilomelane that inwardly was porous and cavernous. Some of the
openings were filled with todorokite
(AM 45.1171).
At the type locality, the Todoroki mine, Yoichi District, Shiribeshi Subprefecture, Hokkaidō Prefecture, Japan, todorokite
forms as a hydrothermal alteration product of inesite and
rhodochrosite (Dana). Other minerals found here include
quartz, rhodochrosite,
pyrite, sphalerite and
galena as well as several alteration products. The Todoroki mine consists of workings on
gold-bearing quartz veins (AM 45.802-807).
In the Syuetu vein, repeated depositions of quartz and
inesite in a fissure were followed by the deposition of
rhodochrosite, chalcedonic
quartz and an inesite-like
zeolite. Most of inesite was replaced by
rhodochrosite, the country rocks of the vein were
kaolinised and pyrite,
sphalerite and galena were precipitated. Then
inesite and the inesite-like
zeolite were decomposed, a dark brown manganese mineral was formed and the
pyrite altered to limonite. The last mineralising
solution deposited many veinlets of calcite. Opal-like
silica, one of the decomposition products, is formed by the oxidation of silicate
(https://rruff.info/rruff_1.0/uploads/JFSHIUS4GM2_289.pdf).
At the Herdade do Ferragudo mine, Castro Verde, Castro Verde, Beja, Portugal, a stalactitic mass of todorokite was found in
a small collection of secondary manganese minerals, chiefly
cryptomelane
(AM 45.1167-1169).
The Smartt mine, Kalahari manganese field, Northern Cape, South Africa. Some of the finest examples of
todorokite have come from the Kalahari manganese field, in particular the Smartt mine. Specimens range in size
from miniature to museum-sized slabs weighing several kilograms. The todorokite occurs as vein-filling vertical
fibres oriented perpendicular to the bedding surfaces of the host rock. Some consist of solid, tightly packed masses;
others contain vuggy zones lined by drusy, colourless, highly lustrous calcite. The
todorokite is intimately associated with manjiroite, and these two
minerals occur in supergene altered low-grade ore. The upper
third section of the orebody consists of
braunite-kutnohorite
mudstone that has bedding-parallel fractures filled by the
asbestiform todorokite and manjiroite. Some of these vein fillings
have vugs lined by drusy calcite and lesser amounts of
chalcedony. Manjiroite is
characteristically black with a dark greenish black streak; todorokite is dark brown with a dull lustre and a
distinctive brown streak. It is suggested that initial bedding parallel fracturing of the orebody was followed, in
sequence, by hydrothermal prograde alteration that first formed manjiroite,
then retrograde alteration formed the todorokite, followed by microshearing of the sequence, and then the final
stage in which the drusy calcite and
chalcedony crystallised in the voids formed during the preceding stages
(R&M 97.6.570-573).
At Sterling Hill, Ogdensburg, Franklin Mining District, Sussex County, New Jersey, USA, todorokite has been identified in
secondary manganese oxides from the old surface workings. It occurs as
soft, dark brownish black masses associated with chalcophanite and
secondary calcite crystals in
altering franklinite-willemite ore
(AM 45.1171).
At Saipan, Northern Mariana Islands, USA, todorokite is intimately admixed with finely divided silica
(AM 45.1170-1171).
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