Study On The Basic Characteristics Of Nacre Layers And Prism-nacre Transition Zone Of Shell

In nature,calcium carbonate is one of the most widespread industrial raw materials,it has a variety of crystal types such as calcite,aragonite and vaterite.Scientists have payed attentions to biogenic carbonate,pearls and shells are the most compelling of bio-mineralization materials which formed by biogenic carbonate.In order to explore the formation mechanism of bio-mineralization materials,we study the mineral composition of Abalone?lamprotula leai and Volsella by using Fourier Transform Infrared spectroscopy(FTIR)and X-Ray diffraction(XRD).Then,we use Scanning Electron Microscope(SEM)and Reflective Microscope to observe the micro-structures of nacre and prism-nacre transition zone of Abalone,Lamprotula leai and Volsella.Last,we analyze the iridescence of Abalone nacre by using Fiber Optic Spectrometer.After these experiments,we got the following results:(1)The basic structure of Abalone is divided into four layers:surface layer,aragonite fiber layer,prismatic and nacre.The main mineral components of the mixture of surface layer and prismatic layer are aragonite and calcite,and the main mineral composition of nacre is aragonite.When aragonite is burned in the temperature of 360?,it will turn into calcite.The aragonite platelets of Abalone nacre are arranged in a type of stacking,and the thickness of aragonite platelets which are in the same area is almost the same.The thickness of mature aragonite platelets nacre at the growing edge of the shell is about 499.00±35.00 nm,and the thickness of mature aragonite platelets at the mature zone of shell is about 371.00±36.00 nm,so the mature aragonite platelets at the growing edge are obviously larger than those at the mature zone of shell.The changing thickness of aragonite platelets is one of reasons for the formation of the iridescence of Abalone nacre.The iridescent of Abalone nacre is a mixture color of blue,red and yellow.(2)The basic structure of Lamprotula leai is divided into three layers:surface layer,prismatic and nacre.The main mineral composition of nacre is aragonite.When aragonite is burned in the temperature of 380?,it will turn into calcite.The aragonite platelets of nacre are arranged in a type of brick-wall.The structure of aragonite platelets at the growing edge is curved,and the thickness of these platelets is about 1.33±0.02 ?m.Then the primary aragonite platelets gradually grow into flat mature platelets,and the thickness of these platelets is about 0.98±0.02 ?m.The thickness of flat mature platelets at the mature zone of shell is about 0.50±0.01 ?m.So,the thickness of aragonite platelets of different regions will change significantly.The transition of prism-pearl layer is a gradual process.The initial aragonite platelets of nacre are formed by horizontal division of prism layer,so their orientations are the same as prismatic layers.(3)The basic structure of Volsella is divided into three layers:surface layer,prismatic and nacre.The structures of primary aragonite platelets at growing edge of shell are curved,and the thickness of these platelets is about 0.66±0.05?m,when the primary aragonite platelets grow into flat mature platelets,the thickness of mature platelets is about 0.30±0.05 ?m.So the primary aragonite platelets are significant larger than the mature ones.The thickness of flat mature platelets at the mature zone is about 0.51 ±0.05 ?m.So,the thickness of aragonite platelets of different regions is different.There is a thin layer named aragonite sphaerocrystal layer between prismatic and nacre,and the curvature radius of this aragonite sphaerocrystal layer is about 16.46±5.00 ?m.The initial aragonite platelets of nacre are formed by horizontal division of aragonite sphaerocrystal layer,so the main mineral composition of nacre is aragonite.