Myriad Mapping of nanoscale minerals reveals calcium carbonate hemihydrate in forming nacre and coral biominerals.

Calcium carbonate (CaCO) is abundant on Earth, is a major component of marine biominerals and thus of sedimentary and metamorphic rocks and it plays a major role in the global carbon cycle by storing atmospheric CO into solid biominerals. Six crystalline polymorphs of CaCO are known-3 anhydrous: calcite, aragonite, vaterite, and 3 hydrated: ikaite (CaCO·6HO), monohydrocalcite (CaCO·1HO, MHC), and calcium carbonate hemihydrate (CaCO·½HO, CCHH). CCHH was recently discovered and characterized, but exclusively as a synthetic material, not as a naturally occurring mineral.

A Molecular-Scale Understanding of Misorientation Toughening in Corals and Seashells.

Biominerals are organic-mineral composites formed by living organisms. They are the hardest and toughest tissues in those organisms, are often polycrystalline, and their mesostructure (which includes nano- and microscale crystallite size, shape, arrangement, and orientation) can vary dramatically. Marine biominerals may be aragonite, vaterite, or calcite, all calcium carbonate (CaCO ) polymorphs, differing in crystal structure.

Loss of biological control of enamel mineralization in amelogenin-phosphorylation-deficient mice.

Amelogenin, the most abundant enamel matrix protein, plays several critical roles in enamel formation. Importantly, we previously found that the singular phosphorylation site at Ser16 in amelogenin plays an essential role in amelogenesis. Studies of genetically knock-in (KI) modified mice in which Ser16 in amelogenin is substituted with Ala that prevents amelogenin phosphorylation, and in vitro mineralization experiments, have shown that phosphorylated amelogenin transiently stabilizes amorphous calcium phosphate (ACP), the initial mineral phase in forming enamel.

Faster Crystallization during Coral Skeleton Formation Correlates with Resilience to Ocean Acidification.

The mature skeletons of hard corals, termed stony or scleractinian corals, are made of aragonite (CaCO). During their formation, particles attaching to the skeleton's growing surface are calcium carbonate, transiently amorphous. Here we show that amorphous particles are observed frequently and reproducibly just outside the skeleton, where a calicoblastic cell layer envelops and deposits the forming skeleton.