Teruggite

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Formula: Ca₄Mg[AsB₆O₁₁(OH)₆]₂.14H₂O
Hydrated hexaborate, arsenic-bearing mineral
Crystal System: Monoclinic
Specific gravity: 2.149 to 2.20 measured, 2.192 calculated
Hardness: 2½
Colour: Colourless to white
Luminescence:
Solubility:
Common impurities:
Environments

Evaporite deposits

Teruggite occurs in lacustrine borate deposits, typically associated with volcanic hot springs and diagenesis of playa sediments. (HOM).

Localities

At the type locality, the Loma Blanca borate deposit, Coranzuli, Susques Department, Jujuy Province, Argentina, the borates are embedded in a local valley fill composed of tuffs, sandstones and conglomerates that reach a thickness of about 25 metres. The pyroclastic rock is a light grey dacitic tuff. A few small fragments of volcanic rocks are also present. The phenocrysts are zoned andesine, quartz, biotite and sanidine; the matrix is composed of the same minerals plus glass and iron oxide. The phenocrysts range in size from one to four millimeters.
Teruggite was found as cauliflower-shaped nodules ranging from 2 to 6 cm in diameter. Each nodule is composed of countless minute euhedral crystals which give the interior a pure-white appearance. Impurities are present as hydrobiotite and montmorillonite confined to small veinlets or nodules of grey colour. The exterior is light brown because of adhering fragments of biotite, feldspar and quartz. The principal minerals found in the deposit associated with teruggite as precipitates from spring waters are inyoite, calcite, ulexite, aragonite and realgar. Only inyoite and calcite are abundant, ulexite is scarce, and the others, including teruggite, are rare (AM 53.1815-1827).
Teruggite from Loma Blanca - Image

At the El Tatio geothermal field, El Loa Province, Antofagasta, Chile, teruggite is the dominant phase in a soft, off-white, poorly-layered and weakly-cemented surface crust, 10 to 15 mm thick, occurring in the high-temperature geothermal field. Other minerals present include halite, which is present throughout but also forms a thin (<0.5 mm), brittle, cratered surface to the deposit, nobleite, ulexite and opal-A, with possible traces of illite-smectite and at least one unidentified phase. Unlike earlier documented occurrences of teruggite, that at El Tatio is evaporitic, modern and surficial (MM 66.2.253–259).

At the Hisarcik Mine, Emet Borate deposit, Emet District, Kütahya Province, Turkey, teruggite is associated with colemanite, meyerhofferite and ulexite (HOM).

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