Sodium sulphate crystallizes in two forms--thenardite and
mirabilite. At high relative humidity (RH), a drop of aqueous sodium sulphate shows on drying tree-like growth of
mirabilite on the substrate outside the drop in addition to crystal formation within the drop boundary (Figure 7(b)).
The presence of layers with more fine texture and salt compositions (gypsum and
mirabilite salt deposits, Fig.
mirabilite, potash, quartz rock, rock phosphate, sandstone, serpentine,
[Na.sub.2]S[O.sub.4] forms two naturally occurring minerals
mirabilite ([Na.sub.2]S[O.sub.4]: 10[H.sub.2]O) and thenardite ([Na.sub.2]S[O.sub.4]).
The formation of the evaporate mineral
mirabilite (N[a.sub.2]S[O.sub.4].10[H.sub.2]O) by brine exclusion was also observed in the deep basins around Sachs Harbour, which indicates that winter formation of sea ice had cut off tidal circulation, producing a hyper-concentrated saline water body (Smith et al., 2007).
Examples of these minerals are ice,
mirabilite, and antarcticite.
Composition and solubility of some common soluble minerals [8] Mineral Compound Solubility, mol/l Calcite CaC[O.sub.3] (calcium carbonate) 0.00014 Gypsum CaS[O.sub.4] x 2[H.sub.2]O 0.0154 (calcium sulphate) -- Ca[Cl.sub.2] x 6[H.sub.2]O 7.38 (calcium chloride) Magnesite MgC[O.sub.3] (magnesium carbonate) 0.001 Hexahydrite MgS[O.sub.4] x 6[H.sub.2]O 4.15 (magnesium sulphate) Epsomite MgS[O.sub.4] x 7[H.sub.2]O 3.07 (magnesium sulphate) Bischofite Mg[Cl.sub.2] x 6[H.sub.2]O 5.84 (magnesium chloride) Washing [Na.sub.2]C[O.sub.3] x 2.77 soda 10[H.sub.2]O (sodium carbonate)
Mirabilite NaS[O.sub.4] x 10[H.sub.2]O 1.96 (sodium sulphate) Thenardite NaS[O.sub.4] (sodium sulphate) 3.45 Halite NaCl (sodium chloride) 6.15 Table 2.
Bloedite [[Na.sub.2]Mg[([SO.sub.4]).sub.2].4[H.sub.2]O],
mirabilite [Na[SO.sub.4].10[H.sub.2]O], rozenite [[Ca.sub.3]([Si.sub.3][O.sub.8][(OH).sub2]], and nesquehonite (Mg[CO.sub.3]) have d-spacings between 3.20 and 3.29 [Angstrom] (JCPDS 1983) and these salts had presumably formed from the basal fertilisers applied to these soils.
When the surface layer of soil dries out in solonchaks that contain sodium sulfate in the soil solution,
mirabilite (Na2SO4x10H2O) crystallizes out of solution, causing the soil matrix to swell and the surface layer of the solonchak to become dry and fluffy.