Abhurite

abhurite

romarchite

hydroromarchite

kutnohorite

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Formula: Sn2+21O6(OH)14Cl16
Hydroxyhalide, tin-bearing mineral
Specific gravity: 4.42
Hardness: 2
Streak: White
Colour: Colourless
Solubility: Dissolves rapidly in nitric acid and slowly in hydrochloric acid Dana
Environments

Hydrothermal environments

Abhurite is formed from the reaction of pure tin with sea water, and has exclusively been associated with tin ingots from shipwrecks. Common associates include aragonite, kutnohorite and romarchite (Mindat). Under the natural saline conditions typical of seawater, romarchite or hydroromarchite is the stable phase; with higher salinity and reduction in pH (more acid environment), the formation of abhurite is favoured (AM 78.235-236).

Localities

At the type locality, Sharm Abhur Cove, Jiddah, Mecca Region, Saudi Arabia, the tin ingot on which the abhurite crystals are found is principally tin, alloyed with minor amounts of copper, lead, bismuth, zinc and antimony. The larger crystals of abhurite form within blisters or pods that contain a viscous mass of liquid and solids. The fluid has an acidity (pH) of 1 (strongly acid). The pods, which cover all the surfaces of the ingot, are up to to 10 mm in size. Abhurite crystals that are unprotected by the blisters formed on the surface of the ingot and were interrupted in their development by a covering of romarchite and a subsequent precipitation of kutnohorite, aragonite and coral. Most of the abhurite contains fragments of the tin alloy and other crystallites (CM 23.233-240).

The Queen Anne's Revenge wreck site, Beaufort, Carteret county, North Carolina, USA. Pewter, a tin-rich alloy, has been widely used for ornamental and utilitarian purposes for the last 400 years because it is durable, relatively easily worked, resistant to corrosion, and similar to silver in appearance. Pewter plates and implements have been recovered and examined from what is believed to be the wreck site of the Queen Anne’s Revenge, flagship of the pirate Blackbeard, that sank near Beaufort, North Carolina in 1718. All of the pewter artifacts from the site display a surface veneer of corrosion products and may be viewed as experiments on tin corrosion that have been continuously in operation for more than 280 years. The corrosion products are composed of romarchite, hydroromarchite and abhurite. The corrosion generally develops in crudely concentric layers, with an inner layer of abhurite in contact with the pewter; the overlying outer layers consist of romarchite and hydroromarchite. Abhurite also occurs as masses of equant grains with abundant small inclusions of residual pewter. Romarchite may be a metastable phase, and is present as the result of slow process of the formation of cassiterite, the most stable tin oxide in most natural environments (CM 41.659-669).

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