HYDROMAGNESITE

    Class : Carbonates, nitrates, borates
    Subclass : Hydrated carbonates
    Crystal system : Monoclinic
    Chemistry : Mg5(CO3)4(OH)2 4H2O
    Rarity : Quite common

Hydromagnesite is found in the same geological context as artinite, essentially in the fissures of serpentinized ultrabasic rocks, where this late-formed hydrothermal mineral lines the surface or occupies the fissures of these rocks. Its name comes from its chemical composition : from the Greek hudôr (water) and magnesite. The crystals are elongated blades with perfect cleavage, almost constantly twinned, which gives them a pseudo-orthorhombic appearance. More rarely, hydromagnesite occurs in acicular crystals, giving fibrous groups, or in massive to powdery aggregates. It is a transparent, colorless to white mineral.

Main photo : Hydromagnesite from Soghan, Arzuiyeh County, Kerman Province, Iran © Rob Lavinsky

Hydromagnesite from Red Mountain Mine, California, USA © Eugene & Sharon Cisneros
Hydromagnesite from U Pustého Mlýna Quarry, Czech Republic © Ondra Kovar
Hydromagnesite from Lobminggraben, Styria, Austria © Yaiba Sakaguchi
Hydromagnesite from Oms, Pyrénées-Orientales, France © Joan Rosell

Hydromagnesite in the World

The most beautiful hydromagnesite crystals come from the chromite mines of Iran, notably that of Soghan : these are exceptional crystals of more than 10 cm assembled in groups of 40 cm by 30 cm. Hydromagnesite is also known associated with artinite in the mines of New Idria and Sulfur Bank (California), and on Long Island (New York). Canadian serpentinites (Kamloops, Atlin) also contain beautiful occurrences. Italy has marbles in which hydromagnesite results from the alteration of periclase (Predazzo, Trentino and Mount Somma, Campania).

Hydromagnesite in France

In France, hydromagnesite is found in Malines (Gard), Oms and the Costabonne mines (Pyrénées-Orientales) as well as at Col du Chenaillet (Hautes-Alpes).

Twinning

Twins are very common on {100} and can be polysynthetic.

Fakes and treatments

No fakes recorded for this mineral species.


Hardness : 3.5
Density : 2.24 to 2.25
Fracture : Undeterminated
Streak : White

TP : Translucent to transparent
RI : 1.523 to 1.545
Birefringence : 0.022
Optical character : Biaxial +
Pleochroism : None
Fluorescence : Blue

Solubility : Acids

Magnetism : NoneRadioactivity : None

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