Todorokite

minerals

birnessite

chalcophanite

cryptomelane

Images
Formula: (Na,Ca,K,Ba,Sr)1-x(Mn,Mg,Al)6O12.3-4H2O
Multiple oxide
Specific gravity: 3.67
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 saponitelévyne-(Ca)offretitechabazite-(Ca)phillipsite-(Ca)aragonitecalcitetodorokite (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).

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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