Abstract
Abstract The partly dehydrated paranatrolite from the Khibiny massif, Russia, Na1.88K0.22Ca0.06[Al2.24Si2.76O10]·2.5H2O, has a space group F1d1 and the unit cell parameters a = 18.6586(5), b = 18.6536(5), c = 6.64119(13) Å, β = 90.199(2)°, and Z = 8. The dominant Na+ cations are located nearby the sodium positions in the natrolite structure. The potassium cations occupy two individual positions. Their different occupancies define the retention of the monoclinic distortion of the structure. H2O molecules statistically occupy eight positions, six being generated with a triple splitting of two positions. Three kinds of main local cation-water assemblages were distinguished, two being similar to the assemblages in the initial high-water paranatrolite. The comparison with the gonnardite and paranatrolite structures determined previously was carried out. Common structural characteristics of natrolite group minerals are suggested from the local water-cation assemblages.
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