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<strong class="journal-contentHeaderColor">Abstract.</strong> This study examines the microbial and geochemical environment surrounding mirabilite (sodium sulfate decahydrate) deposits in Izvorul Tăușoarelor Cave, located in the Romanian Carpathians. Using a metabarcoding approach, we analysed mirabilite, sediments, dipluran insects, drip water, and moonmilk deposits to investigate the microbial communities and elemental profiles linked to mirabilite formation. Elemental analysis revealed a geochemical signature in mirabilite samples that was dominated by sodium, sulfur, and calcium. Microbial profiling revealed a unique pattern: sulfur-reducing bacteria, such as <em>Desulfobacterota,</em> were absent in mirabilite samples, whereas <em>Pseudomonas</em> dominated, suggesting an alternative sulfur cycling pathway that potentially involves sulfide biooxidation. The presence of ammonia-oxidising archaea (<em>Ca. Nitrocosmicus</em>) exclusively in the mirabilite area, and of bacteria (<em>Nitrococcus</em>), indicates a possible influence from a small bat colony, which contributes minimal ammonia that may support the microbial equilibrium required for mirabilite growth. <em>Actinomycetota</em>, abundant in mirabilite, may facilitate mineral crystallisation through mycelium-like structures. We propose the term “microbiocosm” to describe the interconnected network of biotic and abiotic elements surrounding the mirabilite environment, proposing a novel framework for investigating microbial contributions to this mineral formation.