Calcite crystals were nucleated and grown from supersaturated aqueous solutions in the presence of variable concentrations of lithium. The diagram of supersaturation vs [Li+]/[Ca2+] concentration ratio (“morphodrome”) shows a continuous habit variation, from the dominant {011̄1} rhombohedron (at low [Li+]/[Ca2+] ratio) to the dominant {0001} form (at high [Li+]/[Ca2+] ratio). The morphological change is interpreted in terms of two-dimensional layers having the structure of the monoclinic Li2CO3 crystal which are epitaxially adsorbed on the restructured {0001} form of calcite. Hence, even if {0001} is a K form (in the sense of Hartman-Perdok), the corresponding surface behaves like a F form, growing layer by layer from low to high supersaturation values.

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Single microcrystals of Li 2 CO 3 (zabuyelite) were observed on {0001} calcite surfaces, epitaxially grown and oriented along the <210> directions of calcite, the {001} form of zabuyelite being by far the best candidate to form the epitaxial interface. In addition, 3-fold pseudotwins of zabuyelite were observed in epitaxy on the cleavage {101 j 4} rhombohedron surface of calcite. The new twinning law is described along with the most probable zabuyelite/calcite interface. Further, a general rule is proposed, concerning the conservation of the orientation of the carbonate groups across the epitaxial interfaces and twin boundaries in carbonates.