New data on metacinnabar from Tuscany (Italy)

New crystallographic data collected on samples of metacinnabar from the Levigliani mine (Apuan Alps), Niccioleta mine (Metalliferous Hills), and the Monte Amiata Hg ore district are reported. The study of the samples from Levigliani completes the characterization of this phase, integrating the data already available in literature. Its crystal structure has been refined on the basis of single-crystal X-ray diffraction data, achieving a R1 factor = 0.044 on the basis of 43 reflections with Fo > 4σ(Fo). The crystal structure refinement confirms the substitution of Hg by Zn and Fe as well as the contraction of the unit-cell parameter [a = 5.7966(8) Å]. Samples from southern Tuscany do not show any significant chemical substitution. Metacinnabar from the Niccioleta mine was identified on the basis of X-ray powder diffraction only, due to the microcrystalline nature of the available material. The unit-cell parameter was refined on the basis of powder data [a = 5.859(1) Å]. Samples from the Monte Amiata Hg ore district were collected in the Bagnore and Pietrineri mines. Their unit-cell parameters, refined on the basis of single-crystal X-ray diffraction data, are a = 5.8358(14) Å (Bagnore) and 5.8355(5) Å (Pietrineri). The refinement of the crystal structures of samples from Bagnore and Pietrineri converged to R1 = 0.037 and 0.026, respectively. The occurrence of metacinnabar in the ore deposits from Tuscany can be interpreted as an evidence for relatively high temperatures (> 315°C) locally attained during Hg ore formation.