Salt weathering of cement material of the Hussein-Bek Mausoleum (Chishminsky district, Republic of Bashkortostan)

Research subject. Products of salt weathering on limestone building blocks of the Hussein-Bek Mausoleum, located in the Chishminsky District of the Republic of Bashkortostan. Materials and methods. The composition of salt weathering minerals was studied using X-ray phase, electron microscopic, energy-dispersive, and mass spectrometric analysis methods. Results. In the efflorescences, the following main minerals were found: gypsum CaSO 4 × 2H 2 O, hamberstonite K 3 Na 7 Mg 2 (SO 4 ) 6 (NO 3 ) 2 × 6H 2 O, darapskite Na 3 (SO 4 )(NO 3 ) × H 2 O, syngenite K 2 Ca(SO 4 ) 2 × H 2 O, epsomite MgSO 4 × 7H 2 O, kieserite MgSO 4 × H 2 O, glauberite Na 2 Ca(SO 4 ) 2 , dolomite CaMg(CO 3 ) 2 , and celestine SrSO 4 . The sulfur isotope composition (δ 34 S) of the efflorescence minerals ranged from +7.28 to +11.38 ‰ V-CDT. Samples with hamberstonite and darapskite were characterized by light isotope enrichment, which is apparently associated with the biotic impact of bird guano. Conclusions. The main mechanism leading to destruction of the building stone of the HusseinBek Mausoleum was established to be salt weathering of the cement caused by the crystallization of authigenic minerals. The salt weathering of the Mausoleum is ornithogenic in nature, caused by the activity of birds, primarily field sparrows (Passer montanus).