Microscopic plants called coccolithophores (common alga) surround themselves with protective calcite plates; aragonite is used by pteropods (snail-like molluscs) to build their shells and corals use it to make their skeletons which helps form reefs; while some echinoderms, starfish, sea urchins, brittle stars, utilise magnesium calcite
to form their exoskeletons.
Living on a steady diet of copper and tin, the organisms on the statue had "digested" the metals to produce shells with unusual ratios of magnesium calcite
and aragonite, for example, as well as traces of feldspar and quartz.
Being a highly organized network of microscopic channels, the magnesium calcite shell of the sea urchin has a configuration similar to that of a photonic crystal.
The researchers filled the skeleton's pores with a polymer and dissolved the magnesium calcite.
X-ray diffraction analysis of the residue shows quartz as the dominant residue component, with scarcely more than trace quantities of magnesium calcite (Ca, Mg)[CO.
X-ray diffraction analysis of the residue shows quartz as the overwhelmingly predominant residue component, with little more than trace quantities of magnesium calcite, illite, and kaolinite ([Al.
The granules are composed of a fibrous organic matrix in which needle-like low magnesium calcite
crystals are deposited (Neff 1971a).
In the latest of these studies, the scientists found that the sea urchins' teeth contain crystals of magnesium calcite, which are smaller, harder and denser than those of pure calcite.
A matrix of relatively soft calcite fibers holds the harder magnesium calcite crystals, which allows these crystals to spread over the entire surface of the tooth.
Microdolomite inclusions in cloudy prismatic calcites: a proposed criterion for former high magnesium calcites