MICROSTROMATOLITIC DEPOSITS ON GRANITIC MONUMENTS - DEVELOPMENT AND DECAY

Biocolonization and colour change, patina and microstromatolite format ion were studied by analysing the mineralogy, chemistry, petrology and biological activity on two granitic monuments in the Mediterranean ar ea. Based on these analyses and laboratory experiments with isolated m icro-flora, it is concluded that: i) black yeasts and meristematically growing black fungi develop on and within granitic rocks and comprise the same genera and species associated with both marble and limestone monuments; ii) on sheltered but episodically wet surfaces, a surface biofilm or microbial mat gives rise to mineral deposition which traps air-borne dust resulting in a mono- or multilayered patina that can be regarded as a micro-stromatolite or monument stromatolite; and iii) t he main minerals in this patina are calcite, Ca-oxalate, gypsum and Ca -phosphate, none of which is influenced by the substrate, and they mus t thus be regarded as the product of the stromatolite forming micro-fl ora.