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Formula: SiO2.nH2O
Oxide,
paramorph of coesite,
cristobalite, keatite,
quartz, quartz-beta,
seifertite, stishovite,
tridymite, UM2000-61-SiO and
xiexiandeite
Crystal System: Monoclinic
Specific gravity: 2.52 to 2.58 measured, 2.55 calculated
Hardness: 6
Colour: Grey
Environments
Volcanic igneous environments
Basaltic cavities
Mogánite is nearly pure silica, with water contents of ~2 to 3 wt%. It is a common component of
agate, chert and
flint, and is associated with
quartz, chalcedony and
opal
(HOM).
Localities
At Killari, Latur District, Chhatrapati Sambhajinagar Division, Maharashtra, India,
chalcedony, with or without
agate
banding, occurs as amygdaloidal and vein fillings beside zeolites in the
Deccan flood basalts. In samples collected from a depth of 122 metres
in a borehole, mogánite, in addition to α-quartz, has been found.
Mogánite of Killari is associated with amygdaloidal flows containing the
zeolites chabazite,
natrolite,
heulandite and
mordenite, but is absent in flows with
laumontite, indicating the stability of moganite up to the
laumontite zone
(EJM 13.1.127-134).
At the type locality, Mogán, Gran Canaria, Las Palmas Province, Canary Islands, Spain, mogánite is composed
of tightly bound fibres with parallel texture and thickness of 0.1 to 1 microns. The space between is filled with
chalcedony or opal.
Goethite is also associated.
Tridymite is abundant in the
ignimbrites.
The mogánite occurs as nodular masses 1 to 5 cm across in pores and cavities of shear-fissures, or filling
vertical and horizontal cooling cracks as platy masses 1 to 10 mm in thickness in
rhyolitic
ignimbrites
(AM 70.874).
Mogánite from Mogán - Image
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