Ammoniolasalite

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Formula: [(NH₄)₂Mg₂(H₂O)₂₀].[V₁₀O₂₈]
Decavanadate (minerals that contain the [V₁₀O₂₈]^6– polyanion)
Specific gravity: 2.28 measured, 2.278 calculated for the empirical formula and 2.271 for the ideal formula
Hardness: 1
Streak: Light orange
Colour: Bright orange to orange-yellow
Luminescence: Not fluorescent under UV
Solubility: At room temperature slowly soluble in water (minutes) and rapidly soluble in dilute hydrochloric acid (seconds)
Environments

Sedimentary environments
Hydrothermal environments

Ammoniolasalite is a relatively new mineral, approved in 2017 and to date (November 2022) reported only from the type locality.

Localities

At the type locality, the Burro mine, Slick Rock Mining District, San Miguel County, Colorado, USA, the uranium and vanadium ore mineralisation was deposited in sandstone where solutions rich in uranium and vanadium encountered pockets of strongly reducing solutions that had developed around accumulations of carbonaceous plant material. These deposits have been a rich source of secondary vanadium minerals that form from the oxidation of primary vanadium ore minerals at low temperature.
Ammoniolasalite is the newest member of the decavanadate family of minerals. It is moderately rare, and occurs on montroseite- and corvusite- bearing sandstone in an NH₄-rich secondary assemblage also containing ammoniozippeite and the NH₄-bearing decavanadates schindlerite and wernerbaurite. The new ammoniolasalite forms from the oxidation of montroseite-corvusite assemblages in a moist environment. Mining operations have exposed both unoxidised and oxidised phases. Under ambient temperatures and generally oxidising near-surface conditions, water reacts with pyrite to form aqueous solutions with relatively low pH (acid). The various secondary vanadate phases that form depend upon prevailing conditions and the presence of other cations such as (NH₄)⁺, Na⁺, Ca²⁺, Mn²⁺ and Pb²⁺. The (NH₄)⁺ presumably derives from organic matter in the deposit
Crystals of ammoniolasalite occur as short prismatic to equant crystals, often exhibiting stepped or skeletal faces. The crystals are bright orange to orange-yellow, with a light orange streak and a vitreous lustre (CM 56.6.859-869).

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