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
