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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
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 -
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