Department of Science and Technology, Meiji University, 1-1-1 Higashimita, Tama-ku, Kawasaki 214-8571, Japan.
J Struct Biol. 2011 Oct;176(1):91-6. doi: 10.1016/j.jsb.2011.06.011. Epub 2011 Jul 6.
To understand the formation mechanism of crossed lamellar structures in molluskan shells, the crystallographic structural features in the shell of a bivalve, Meretrix lamarckii, were investigated using scanning electron microscopy, electron backscattered diffraction, and transmission electron microscopy with a focused ion beam sample preparation technique. Approximately 0.5 μm-thick lamellae (the second-order units) are piled up obliquely toward the growth direction to form the first-order unit and the obliquity is inverted between adjacent units along the shell thickness direction. The first-order units originate around the center of the shell, initially growing parallel to the shell and subsequently curving toward the inner or outer surfaces. The lamellae consist of aragonite granular and columnar layers, which group together to adopt the same crystal orientation forming crystallographic units (crystallites). Multiple {110} twins are common both in the granular and columnar layers. The crystallite c-axis is parallel to the columns and is inclined at angles 0-50° from the lamellar normal (dispersing among individual lamellae), toward the shell growth direction. Probably, the directions of the a- and b-axes are random in the lamellae, showing no specific orientation.
为了理解软体动物贝壳中交错层状结构的形成机制，我们利用扫描电子显微镜、电子背散射衍射以及聚焦离子束样品制备技术的透射电子显微镜，研究了双壳贝类贻贝贝壳的晶体结构特征。厚度约为 0.5μm 的薄片（二阶单元）以相对于生长方向倾斜的方式堆积，形成一阶单元，并且在沿壳厚度方向的相邻单元之间，倾斜方向发生反转。一阶单元围绕贝壳的中心产生，最初与贝壳平行生长，随后向内部或外部表面弯曲。薄片由文石颗粒和柱状层组成，它们聚集在一起采用相同的晶体取向形成结晶单元（晶体）。颗粒层和柱状层中都普遍存在{110}孪晶。晶体的 c 轴与柱状层平行，与层片法线成 0-50°的夹角（在单个层片中分散），朝向贝壳的生长方向。可能在薄片中，a 轴和 b 轴的方向是随机的，没有特定的取向。
