3.1.6. Sample OM51

The sample is characterized by anhedral calcite grains that compose a heteroblastic fabric ("mortar" type, Figure 16a). The majority of these crystals are characterized by sutured and minor embayed grain boundaries (Figure 16b). Maximum grain size reaches up to 2.3 mm. Bent twinning lines in calcite crystals are common, indicating tectonic deformation. Accessory phases include minor dolomite, mica group minerals (phlogopite/muscovite), apatite and pyrite (Figure 16c,d) which forms round-shaped grains included in calcite.

**Figure 16.** Transmitted (**a**–**c**) and reflected (**d**) light microphotographs of sample OM51: (**a**) heteroblastic fabric ("mortar") in calcite grains (Cal) most of which exhibit polysynthetic twinning. Minor phlogopite (Phl) is also present, crossed-polarized light; (**b**) calcite (Cal) crystals with partly sutured and embayed grain boundaries, plane-polarized light; (c) anhedral apatite (Ap) crystal included in calcite (Cal), crossed-polarized light; (**d**) round-shaped pyrite (Py) crystal included in calcite (Cal).

The above described microscopy results are summarized in Table 3, where the mineralogical content, the fabric, as well as the MGS and GBS parameters are stated.


**Table 3.** Petrographic features and mineralogical content of the studied samples.

Abbreviations: Cal = calcite; Dol = dolomite; Phl = phlogopite; Ap = apatite; Py = pyrite, HE = heteroblastic; MGS = maximum grain size in mm; GBS = grain boundary shape. Maximum grain size (MGS). Values with (\*) refer to calcite grains from grey-colored bands.
