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Formula: (NH4)Fe3+3(SO4)2(OH)6
Anhydrous sulphate containing hydroxyl, alunite group,
alunite supergroup
Crystal System: Trigonal
Specific gravity: 3.112 calculated
Hardness: 3½ to 4½
Colour: Light yellow; light yellow to nearly colourless in transmitted light
Solubility: Soluble in hot hydrochloric acid
Environments
Sedimentary environments
Coal-Seam fires
Localities
At the Dębieńsko Mine heap, Gmina Czerwionka-Leszczyny, Rybnik County, Silesian Voivodeship, Poland,
ammonioalunite, ammoniojarosite and their solid-solution
series were found on a burning coal dump. The minerals occur as yellow, fine-grained crusts and botryoidal masses
in the outer part of a sulphate crust found about 1 m below the surface. The crust is composed mainly of
godovikovite and
tschermigite that formed by interaction of sour (containing
significant amounts of hydrogen sulfide) fire gases or solutions and waste materials beneath the surface of the
burning coal dump at temperatures of at least 80°C to 100°C. The crystals often reveal oscillatory zoning due to
different aluminium and iron
contents in thin bands. It is suggested that a complete solid solution between
ammonioalunite and ammoniojarosite exists in nature
(MM 74.4.731–745).
At the Zlatá Baňa deposit, Zlatá Baňa, Prešov District, Prešov Region, Slovakia, ammoniojarosite is
associated with aluminite and
natrojarosite
(HOM).
At the type locality, the Kaibab fault, Kane County, Utah, USA, ammoniojarosite occurs in black
lignitic shale
containing pyrite. The ammoniojarosite forms small lumps and hard
irregular flattened nodules up to 4 centimetres broad by 5 millimetres thick embedded in blackish-brown
lignitic material. They frequently enclose small grains of the
lignite and fibrous patches of
tschermigite. Other associated minerals include
epsomite and jarosite
(AM 12. 424-426).
At the I90 roadcut, Buffalo, Johnson County, Wyoming, USA, ammoniojarosite has been found in
black to brown shale of Eocene age (55.8 to 33.9 million years ago),
about 15O m south of an area slightly altered by the burning of a coal bed. The ammoniojarosite occurred as
an earthy, pale ocherous yellow powder coating on selenite crystals. The
selenite crystals occur as vertical fracture-filling material within the
shale
(CM 20.91-95).
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