Zeolites are hydrated aluminosilicates of calcium, sodium, potassium and more rarely barium, strontium and magnesium with the general formula:
(Li, Na, K)a (Mg, Ca, Sr, Ba)b Al(a=2b) Sin-2b) O2n m.H2O
Whitish in color, these minerals are often associated with calcite and chlorite.
Ain Temouchent Alkali basalts (western Algeria) contain nodules of variable size (millimeter to 20 cm) and the vacuoles occupy faults and joints.
Due to the difficulty to distinguish minerals with the polarizing microscope, our study is mainly based on data from chemical analysis (electron microprobe) and RX diffraction.
Three zeolitic species were distinguished by RX: para natrolite, natrolite and thomsonite.
The microprobe analysis revealed the presence of thomsonite and mesolite in a same vacuole.
Reports Ca / Ca + Na to Si / Si + Al analyzed of thomsonites allow highlighting the lamellar (bladed) of these zeolites, and the absence of pseudo-tetragonal and botryoidal forms.
These thomsonites, like the most of zeolites comes from the intense hydrothermal alteration of primary minerals (olivine, plagioclase and augite) following the intense leaching of alkalis (Na, Ca, Mg, K) the increasing pH and alkalinity of the fluids contained and the pores and vacuoles.
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