A cave in granitic rocks was studied in Mezesse, South Cameroon. Coralloid speleothems, draperies and dissolution traces on the cave walls attest to its truly karstic nature. The speleothems consist of microlayers of opal and taranakite (K,NH4)Al3(PO4)3(OH).9H2O. They indicate a significant mobilization of silica, Al and K from granite during the formation of the cave. Identification of silicified bacteria in the speleothems layers suggests a possible role of these micro‐organisms in silica deposition. The presence of taranakite and of silicified organic remains within the speleothems lead to a better understanding of the genesis of the cave.

Gehlenite is a common mineral in three high-temperature calcic skarns in Romania: Măgureaua Vaţei and Cornet Hill in Apuseni Mountains and Oraviţa in Banat. In all three occurrences, a gehlenite zone occurs within the contact between dioritic or monzodioritic bodies of Upper Cretaceous age and carbonaceous sequences of Mesozoic age. The melilite solid-solutions vary from Ak 34.1 to Ak 51.2 (mean Ak 41.2 ) at Oraviţa, from Ak 30.4 to Ak 42.9 (mean Ak 38.3 ) at Măgureaua Vaţei, and from Ak 24.3 to Ak 41.7 (mean Ak 32.9 ) at Cornet Hill, respectively. The content of "Na-melilite" is low, from up to 1.96 mol.% at Cornet Hill to up to 3.60 mol.% at Oraviţa. The cell parameter a ranges from 7.679(3) to 7.734(3) Å at Oraviţa, from 7.683(4) to 7.735(1) Å at Măgureaua Vaţei, and from 7.684(3) to 7.733(1) Å at Cornet Hill, whereas c varies from 5.043(3) to 5.065(3) Å at Oraviţa, from 5.040(1) to 5.070(3) Å at Măgureaua Vaţei, and from 5.044(1) to 5.067(4) Å at Cornet Hill. It is not possible to quantify the variations in the crystallographic parameters by considering only the åkermanitic substitution because the "Na-melilite" and "Fe-åkermanite" substitutions also play an important role. The cell parameter a remains practically constant within experimental errors, in spite of the increasing åkermanite-for-gehlenite substitution, due to the opposite influence of the "Na-melilite" component. The åkermanite substitution prevails over the opposite influence of "Na-melilite" in increasing the cell volume, and is additive to the influence of "Na-melilite" in decreasing the cell parameter c. The record in the infrared-absorption spectra of bands located at ~855 cm -1 and ~670 cm -1 , respectively, which may be tentatively assigned to Al-O-Al stretching, is indicative of the presence of gehlenite-rich members of the melilite group in all the three occurrences.

Omongwaite, Na 2 Ca 5 (SO 4 ) 6 .3H 2 O, is a new mineral, found as inclusions in gypsum crystals in recent salt lake deposits at Omongwa pan, Namibia. It is monoclinic, with space group C2, a = 12.08(3) Å , b = 6.96(1) Å , c = 6.39(2) Å , ß = 90.2(3)º, V = 537(2) Å 3 , and Z = 1. The six strongest lines in the X-ray powder diffraction pattern [d obs . (Å ), (I/I o meas. ), (hkl)] are: 6. Electron microprobe analysis, recalculated on the basis of 3H 2 O per formula unit (p.f.u.), gave 56.16 wt.% SO 3 , 30.82 wt.% CaO, 5.25 wt.% Na 2 O, 3.21 wt.% K 2 O, 6.25 wt.% H 2 O, totalling 101.69 wt.%. The empirical formula, based on 24 anhydrous oxygens p.f.u., is (Na 1.47 K 0.59 ) S=2.06 Ca 4.76 S 6.07 O 24 .3H 2 O, yielding Na 2 Ca 5 (-SO 4 ) 6 .3H 2 O as the end-member formula. Na/K ratios are variable, with an average of~2.5. The crystals are elongated, with pseudohexagonal transversal cross-sections and with sphenoidal terminations that are commonly developed at one end. The crystal structure of omongwaite is similar to that of bassanite, CaSO 4 .0.5H 2 O. Published studies of the synthetic phase show that it can be described as a bassanite structure in which one out of six Ca 2+ ions are replaced by Na + and a second Na + ion occupies a position near those sites. The crystals are parallel to the [001] axis of the gypsum crystals in which they occur as inclusions. The mineral formed by topotactic replacement during interaction of gypsum with concentrated solutions. It is preserved where the affected surface became covered by gypsum by rapid growth shortly after the formation of omongwaite. The mineral is named after the locality where it was found.

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We measured nuclear forward scattering of synchrotron radiation by the 68.7 keV nuclear resonance of 73Ge with a half-life . The Debye temperatures of CaGeO3 in the wollastonite, garnet and perovskite phases were determined to be 386(20) K, 437(20) K and 507(20) K, respectively, and 309(20) K and 459(11) K for GeO2 in the quartz and rutile phases, respectively. The isomer shift is clearly dependent on the Ge valence but not directly on the coordination geometry. The so far unknown magnetic moment μe of the 68.7 keV excited state of 73Ge is determined to be . Time domain 73Ge Mössbauer spectroscopy with the 68.7 keV resonance is feasible for isomer shift and Debye temperature measurements but so far neither electric quadrupole nor magnetic hyperfine interactions could be observed.