The　mechanism　of　nacre　formation　in　gastropods　involves　a　vesicular　system　that　transports　organic　and　mineral　precursors　from　the　mantle　epithelium　to　the　mineralization　chamber.　Between　them　lies　the　surface　membrane,　a　thick　organic　structure　that　covers　the　mineralization　chamber　and　the　forming　nacre.　The　surface　membrane　is　a　dynamic　structure　that　grows　by　the　addition　of　vesicles　on　the　outer　side　and　recedes　by　the　formation　of　interlamellar　membranes　on　the　inner　side.　By　using　a　combination　of　electron　microscopy　imaging　and　spectroscopy,　we　have　monitored　the　journey　of　the　vesicles　from　the　mantle　epithelium　to　the　mineralization　chamber,　focusing　on　the　elemental　composition　of　the　organic　structures　at　each　stage.　Our　data　reveal　that　transport　occurs　in　lipid　bilayer　vesicles　through　exocytosis　from　the　outer　mantle　epithelium.　After　release　into　the　surface　membrane,　chitin　undergoes　a　process　of　self-assembly　and　interaction　with　proteins,　resulting　in　progressive　changes　of　the　internal　structure　of　the　surface　membrane　until　the　final　structure　of　the　interlamellar　membranes　is　acquired.　Finally,　these　detach　from　the　inner　side　of　the　surface　membrane.　Elemental　analysis　revealed　the　transport　of　a　considerable　amount　of　calcium　bound　to　proteins,　likely　forming　calcium-protein　complexes.　Statement　of　significance:　The　formation　of　nacre　tablets　occurs　through　the　incorporation　of　organic　and　mineral　precursors　extruded　from　the　mantle　epithelium.　Although　much　attention　has　been　paid　to　the　presence　of　amorphous　phases　in　recent　decades,　the　calcium　transport　system　has　not　yet　been　elucidated.　We　have　monitored　the　packaging　of　organic　and　mineral　precursors　in　the　form　of　vesicles　from　the　mantle　epithelium　to　the　mineralization　chamber.　We　have　shown　that　the　surface　membrane　represents　the　zone　where　chitin　and　protein　polymerization　takes　place,　acquiring　the　final　structure　for　the　formation　of　interlamellar　membranes.　Interestingly,　these　organic　structures　transport　a　considerable　amount　of　organic　calcium　into　the　mineralization　chamber,　which　support　a　transport　system　based　on　acidic　calcium-binding　proteins.