Koenenite=[Mg7AI4(OH)22]4+.[Na4(Ca,Mg)2CI12]4- , is a
typical non-silicate clay mineral of oceanic salt deposits
which also widely occurs in salt clay, anhydrite, halite, and
potash-bearing rocks. Koenenite is found as an
undesirable sludge-forming component in the processing
of potassium salts .
Koenenite was first reported, in 1902, as an impurity
in a fairly pure halite from the Justus! potash mine, near
Volpriehausen/Sollingen in northern Germany. Since
NaCI was considered to be presented only as halite, the
chemical composition of koenenite was wrongly given as
2MgCl2 5Mg(OH)2 Al(OH)3 . But an accurate
composition of the mineral should be given as 4NaCI
4(Ca, Mg)Cl2 5Mg(OH)2 4AI(OH)3 . At present time,
koenenite is the only naturalIy occuing basic Mg-AI
chloride (Plus additional NaCI).
The initial experiments for the synthesis of koenenite
was carried out in 1982, in the system
NaCI-MgCl2-CaCl2-Al2O3-MgO-(H2O) at temperatures
between 2OO•C and 5OO•C and a pressure of one kilobar.
It was observed that firstly, the chemical composition
of the choride layer could range from [Na4 (Ca,
Mg)2CI12]4- to [Ca4?2CI12]4-, and secondly, it is possible to
form calcium-free koenenite.
Finally, in 1985 synthesis of Ca-free koenenite was
successfully carried out by the author at temperatures of
zoo' C-4OO• C and pressures of 1oo-1000 bars, in the
following two systems:
1.NaCI-MgClz-Al2O3-MgO-H20
2.NaCl-MgCI2-H2O-Ul(1)
)