Nanoscale Analysis of the Structure and Composition of Biogenic Calcite Reveals the Biomineral Growth Pattern

The vast majority of calcium carbonate biocrystals differ from inorganic crystals in that they display a patent nanoroughness consisting of lumps of crystalline material (calcite/aragonite) surrounded by amorphous pellicles. Scanning transmission electron microscopy coupled with electron energy loss spectroscopy (STEM-EELS) was used to map the calcite secreted by a barnacle chemically and structurally with ultrahigh resolution (down to 1 nm). The material is composed of irregular lumps of calcite (up to two hundred nm in diameter) surrounded by relatively continuous cortexes (up to 20 nm thick) of amorphous calcium carbonate (ACC) and/or nanocalcite plus biomolecules, with a surplus of calcium relative to carbonate. We develop a model by which the separation of the crystalline and amorphous phases takes place upon crystallization of the calcite from a precursor ACC. The organic biomolecules are expelled from the crystal lattice and concentrate in the form of pellicles, where they stabilize minor amounts of ACC/nanocalcite. In this way, we change the previously established conception of biomineral structure and growth.

Automated summary

The majority of calcium carbonate biocrystals have a nanoroughness consisting of crystalline lumps surrounded by amorphous pellicles. Using STEM-EELS, the calcite secreted by a barnacle was mapped with ultrahigh resolution. The material is composed of irregular calcite lumps surrounded by cortexes of amorphous calcium carbonate and/or nanocalcite plus biomolecules. The separation of the crystalline and amorphous phases takes place during calcite crystallization from a precursor ACC, which differs from the previously established conception of biomineral structure and growth.