Juansilvaite

juansilvaite

anhydrite

canutite

halite

Images

Formula: Na5Al3[AsO3(OH)]4[AsO2(OH)2]2(SO4)2.4H2O
Hydrated arsenate-sulphate
Crystal System: Monoclinic
Specific gravity: 3.01 measured, 3.005 calculated
Hardness: 2½
Streak: White
Colour: Bright pink (crystals), dull pale pink (opaque aggregates)
Luminescence: Does not fluoresce under UV
Solubility: Slowly soluble in dilute hydrochloric acid at room temperature
Environments


Hydrothermal environments

Juansilvaite is a relatively new mineral, approved in 2015.

Localities

The type locality is the Torrecillas mine, Iquique, Iquique Province, Tarapacá, Chile. The Torrecillas deposit consists of two main veins rich in secondary arsenic and copper minerals that intersect metamorphosed marine shales and lavas. The juansilvaite occurs as a secondary alteration phase in association with anhydrite, canutite, halite, sulphur, and a mahnertite-like phase. The secondary assemblages at the Torrecillas deposit have formed from the oxidation of native arsenic and other arsenic-bearing primary phases, followed by later alteration by saline fluids derived from evaporating meteoric water under hyperarid conditions.
Juansilvaite occurs as blades up to ∼0.5 mm long grouped in tightly intergrown radial aggregates, or as opaque rounded aggregates. It is bright pink, transparent with a white streak and vitreous lustre. It is brittle with irregular fracture and very good cleavage. No twinning was observed (AM 103.833).
Juansilvaite from the Torrecillas mine - Image

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