In the scope of the France-Greek program PLATON n° 30409XH “EMerChanCy”, this work focuses on the beachrocks of Paros and Naxos Islands, in central Cyclades, Aegean Sea, Greece, in an attempt to study their geochemistry and interpret their palaeoenvironmental significance. Beachrocks are coastal sedimentary formations, consisting of beach sediments that are relatively quickly cemented through the precipitation of CaCO₃. However, debate still exists concerning their depositional environment, and therefore, their use as indicators for sea-level changes. For the aim of the present study, representative bulk samples from both islands were analyzed for their mineralogical (XRD) and chemical compositition (SEM). Chemical analyses were performed by XRF . The cement agent and the fine sand/clay fraction of the samples mainly consist of authigenic magnesian calcite, which commonly precipitates in shallow marine environments, especially in high concentration of Ca²⁺(>4 mol% CaCO₃ or 1.2 wt.%). Furthermore, a series of clastic silicate and alumino-silicate minerals are detected. The predominant coarse fragments hosted within cement material are quartz, albite and K-feldspar. The texture of the beachrock samples varies from almost homogeneous sandstone to a mixture of lithologies, such as massive gravel, sandstone and claystone. Most of the grains are flattened and only rarely angular pieces of siliceous rocks occur, hosted in the fine-grained Mg-calcite cement. This grain size and shape is indicative of the genetic environment of beachrocks, implying the maturity level of cementation from early stage to modern situation. The beachrock samples derived from various depositional periods and depths, from the front and end slabs. The beachrocks were also correlated with stratigraphical material from boreholes and archaeological remains from the study area in an attempt to understand the coastal changes during the late Holocene in Central Cyclades.