TODOROKITE

    Class : Oxides and hydroxides
    Subclass : Hydroxides and hydrates
    Crystal system : Monoclinic
    Chemistry : (Mn,Ca,Mg)Mn3O7 H2O
    Rarity : Quite common

Todorokite is a complex oxide of manganese (in the form of Mn4+). It has a crystal structure close to that of hollandite and romanechite, but with larger vacancies that accept larger cations (Mg2+, Mn2+, Cu2+, Ca2+...), which explains its more fluctuating chemistry. Todorokite is mainly a secondary mineral resulting from the supergene oxidation of manganese carbonates and silicates. It is also a mineral of submarine fumarolic deposits, and especially the main manganese mineral of manganese nodules on the ocean floor. Its name comes from its discovery site : the Todoroki mine (Japan). Todorokite is grey to purplish grey in colour, with a slightly greasy metallic luster. It occurs as spongy reniform masses, often with a concentric banded texture, consisting of minute lamellar crystals, in fibrous aggregates or in fine coatings. It is locally an important manganese ore.

Main photo : Todorokite from Smartt Mine, South Africa © Bruce Cairncross

Todorokite in the World

Among the many terrestrial todorokite deposits, the Hotazel manganese district (South Africa) should be particularly mentioned, which has yielded extraordinary asbestiform crystals up to 15 cm, frequently grouped in sheaves, and fibrous masses bearing rhodochrosite crystals of 1 cm. It is an important manganese ore in the mines of Cuba and Ghana (Nsuta). It is also known from the large Sterling Hill deposit (New Jersey), Todoroki (Japan) and several Australian deposits.

Right photo : Todorokite and calcite geodes from Smartt Mine, South Africa © Bruce Cairncross


Todorokite in France

In France, todorokite is known from the Vallée d'Aure (Hautes-Pyrénées) at Fumade (Tarn), at Saphoz (Haute-Saône), in the manganese deposit of Romanèche-Thorins (Saône-et-Loire) and in Tahiti.

Twinning

Contact twinning is known.

Fakes and treatments

No fakes listed for this mineral species.


Hardness : 1.5
Density : 3.67
Fracture : Splintery
Streak : Brown to black

TP : Opaque
RI : 2.310 to 2.350
Birefringence : -
Optical character : Biaxial -
Pleochroism : Visible
Fluorescence : None

Solubility : Hydrochloric acid

Magnetism : NoneRadioactivity : None

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