The mineralogical features of the substrate were generally considered a min
or factor in structuring marine benthic communities. The aim of this work i
s to verify whether the presence of quartz minerals in rock may explicate d
ifferences, usually explained in terms of substrate roughness or other fact
ors, in epibenthic communities. Laboratory tests on the hydroid Eudendrium
glomeratum showed that its planulae settle preferentially on carbonatic, ra
ther than quartzitic, substrates. To test the influence of quartz on establ
ished communities, we analysed the species composition and quantitative str
ucture of sublittoral sessile assemblages on different rocks in several loc
alities of the Ligurian and Tyrrhenian seas. The observed differences appea
red to be related to the presence of quartz in the substrate rock. The inte
ractions between organisms and minerals (bio-mineralogy) might play a signi
ficant role on benthic communities, affecting not only the initial colonisa
tion, but also later assemblages. This potential role has been largely negl
ected to date and further studies are needed to prove its importance.