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Fiona C. Meldrum and Helmut Cölfen chalk up some of the myriad forms and uses of calcium carbonate to burnish a ‘dull’ reputation.

The term mesocrystal describes three-dimensional crystals formed by oriented assembly and that exhibit nanoparticle substructures. Here, the authors perform detailed structural analyses on synthetic calcium carbonate/polymer crystals, and show that common signatures used to assign mesocrystals may be unreliable.

Biominerals exhibit properties, morphologies and hierarchical ordering that invariably surpass those of their synthetic counterparts. Artificial biominerals consisting of calcite crystals incorporating copolymer micelles have now been produced. The synthetic crystals show analogous texture and defect structures to biogenic calcite crystals and are harder than pure calcite.

The occlusion of biomacromolecules can endow biominerals with enhanced mechanical properties. Here, the authors usein situatomic force microscopy and micromechanical simulations to trace micelle incorporation in calcite to shed light on the mechanism of occlusion and cavity formation.

By means of a model of calcite single crystals containing high and tunable amounts of occluded amino acids, the hardness of the crystals can be quantitatively correlated with their composition.

Epitaxial crystal growth attracts significant interest. Here, the authors use Bragg Coherent Diffraction Imaging to demonstrate calcite crystal precipitation on self-assembled monolayers exhibiting single dislocation loops with different geometries to those generated in conventional epitaxial thin films.

The crystallization of amorphous calcium carbonate is a widely studied process. Here, the authors probe the mechanism and show that transformation to calcite is preceded by dehydration, even in solution, and that loss of the final water fraction triggers crystallization.

Materials exhibiting room temperature phosphorescence (RTP) with short afterglow are desirable for bio-medical applications. Here the authors synthesise a library of compounds with tunable RTP properties, embedding carbon nanodots in non-toxic alkaline-earth carbonate, sulphate and oxalate hosts.

Mineralized collagen is the building block of bone but how the collagen directs hydroxyapatite formation remains unclear. Here, the authors demonstrate cylindrical pores in collagen and how the anisotropic growth of hydroxyapatite directs the orientation of crystal growth in mineralized collagen.

It is demonstrated that Bragg coherent diffraction imaging can be used to visualize dislocation propagation in three dimensions during the repeated growth and dissolution of calcite crystals.

Introducing organic guests to a crystal is a convenient way to tailor its properties. Here, the authors occlude fluorescent dyes within calcite to reveal that additives can occupy distinct zones of a crystal, and strategically embed green, blue, and red dyes to create white fluorescent calcite.

Calcium carbonate biomineralisation has long been linked to acidic macromolecules. Here, the authors challenge this view and show that a huge number of gold nanoparticles coated with hydroxyl-rich proteins can be incorporated into a calcium carbonate crystal while maintaining single crystal character.