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Formula: Ni2+4.5(AsO4)3
Anhydrous arsenate of nickel,
monoclinic paramorph of tetragonal
niasite,
alluaudite supergroup, probably
alluaudite group
Crystal System: Monoclinic
Specific gravity: 4.801 calculated for the empirical formula, and 4.808 calculated for the ideal formula
Hardness: 5
Streak: Pale orange
Colour: Pink-orange
Luminescence: No fluorescence observed under long wave or short wave UV
Solubility: In dilute hydrochloric acid at room temperature johanngeorgenstadtite rapidly loses colour,
indicating decomposition, and slowly dissolves
Environments
Johanngeorgenstadtite is a relatively new mineral, approved in 2019 and to date (October 2024) reported only from
the type locality.
Localities
At the type locality, Johanngeorgenstadt, Erzgebirgskreis, Saxony, Germany, johanngeorgenstadtite and its
paramorph niasite were found,
associated with aerugite, bunsenite,
quartz, rooseveltite and
xanthiosite, in granular intergrowths. The assemblage is apparently
secondary in origin and most likely formed from the breakdown of
primary nickeline under
low humidity and oxidising conditions.
Johanngeorgenstadtite occurs in sugary aggregates of pink-orange irregular, rounded grains or short prisms that
are about 70 µm in diameter. No forms could be determined and no twinning was observed. The streak is pale pink.
Crystals are transparent with resinous to subadamantine lustre, brittle with curved and stepped fracture. Multiple
cleavage planes are apparent
(EJM 32.3.373-385).
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