Metathénardite

metathenardite

vanthofferite

johillerite

lammerite

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Formula: Na2(SO4)
Anhydrous sulphate, paramorph of thénardite
Crystal System: Hexagonal
Specific gravity: 2.72 measured, 2.717 calculated
Hardness: 3
Streak: White
Colour: Colourless, white, light blue, greenish, yellowish, greyish or brownish
Solubility: Dissolves in water at room temperature
Environments

Fumeroles

Metathénardite is a high-temperature, hexagonal mineral approved in 2016. All specimens with metathénardite were collected from areas with temperatures of 350 to 400°C (Mindat).

Localities

There are three co-type localities, the Arsenatnaya fumarole, the Glavnaya Tenoritovaya fumarole, and the Yadovitaya fumarole, all at the Second scoria cone, Northern Breakthrough, Great Fissure eruption, Tolbachik Volcanic field, Milkovsky District, Kamchatka Krai, Russia.

The holotype specimen was found in the Glavnaya Tenoritovaya fumarole; later the mineral was identified in several other Tolbachik fumaroles. It is a common sulphate mineral in high-temperature exhalations of the three active fumaroles Glavnaya Tenoritovaya, Yadovitaya and Arsenatnaya. Metathénardite samples from the Yadovitaya and Arsenatnaya fumaroles that are considered to be cotypes. Specimens with metathénardite were collected from hot zones of all three fumaroles. The temperatures in these areas varied from 350 to 400oC.
The holotype metathénardite from the Glavnaya Tenoritovaya fumarole is associated with hematite, tenorite, fluorophlogopite, sanidine, anhydrite, krasheninnikovite, vanthoffite, glauberite, johillerite and lammerite. The secondary, supergene association includes gypsum, blödite, and powdery aggregates of unidentified sulphates. At this location the metathénardite occurs as interrupted crusts up to 2 x 2 cm2 in area and up to 0.2 mm thick overgrowing basalt scoria or thin incrustations of fluorophlogopite and hematite covering the surface of basalt scoria. The crystals and grains of metathénardite forming the crust commonly contain abundant dust-like inclusions of hematite.
The cotype from the Arsenatnaya fumarole is typically associated with hematite, tenorite, fluorophlogopite, sanidine, euchlorine, wulffite, anhydrite, fluoborite, johillerite, nickenichite, calciojohillerite, badalovite, tilasite, cassiterite and pseudobrookite. At this locality the metathénardite forms abundant crystal crusts and brushes up to several hundred cm2 in area, typically open-work, in cavities between blocks of basalt scoria and volcanic bombs. The crystals are up to 3 mm across and up to 1 mm thick.
The cotype metathénardite from the Yadovitaya fumarole is associated with tenorite, euchlorine, fedotovite, dolerophanite, langbeinite, krasheninnikovite, anhydrite and hematite. Metathénardite here is a widespread mineral forming clusters, incrustations, and brushes up to 20 cm2 in area of hexagonal tabular crystals (CM 57.6.885-901).

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