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Formula: Ca4Al2(OH)12(CO3).5H2O
Hydroxide, hydrocalumite group,
hydrotalcite supergroup
Crystal system: Triclinic
Specific gravity: 2.180 calculated
Colour: Colourless
Environments
Metamorphic environments
Hydrothermal environments
Mampsisite is a new mineral, approved in 2023 and to date (May 2026) reported only from the type locality.
Localities
At the type locality, the Amoraite type locality, Hatrurim Basin, Tamar Regional Council, Beersheba Subdistrict,
Southern District, Israel, mampsisite was discovered in peralkaline hydrothermal assemblages confined to
pyrometamorphic rocks of the Hatrurim Basin in the Negev Desert, near the Israeli coast of the Dead Sea. The
mampsisite occurs in the cavities of marble-like
larnite - brownmillerite -
jasmundite rock; associated minerals
include katoite, portlandite,
and other natural layered double hydroxides, namely kuzelite,
hydrocalumite and
mariakrite. The assemblage was formed from residual highly alkaline
solutions produced by late hydrothermal alteration of larnite and
jasmundite. Mampsisite forms colourless platy crystals up to 50 μm
across with one perfect cleavage.
The crystal structure represents an ordered 1:1 interstratification of two kinds of fully ordered layered units:
the positively charged, carbonate-free hydrocalumite layer
[Ca4Al2(OH)12(H2O)4]2+ and a negatively charged layer
of previously unknown type
[Ca4Al2(OH)12(H2O)2(CO3)2]2−.
The counter-charged layers are separated by two H2O molecules per formula unit, which are lying in the
interlayer
(AM 111.5.826–835).
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