3.1.2. Sample OM11

Calcite is the dominant mineral component of the sample and forms subhedral porphyroblastic crystals (MGS 1.7 mm) surrounded by smaller neoblasts (Figure 12a). The fabric is strongly heteroblastic, (mortar-type, Figure 12a) and many crystals display intense polysynthetic twinning. In some cases, twinning lines are bent, a fact that indicates tectonic deformation. Calcite grains usually display sutured boundaries, but in places embayed boundaries were also observed (Figure 12b,c) Phlogopite, apatite and pyrite, which forms round-shaped grains, were identified as accessory phases (Figure 12b–d).

**Figure 12.** Transmitted (**a**–**c**) and reflected (**d**) light microphotographs of sample OM11: (**a**) Heteroblastic fabric ("mortar"), crossed-polarized light; (**b**) sutured calcite (Cal) grain boundaries. At places calcite includes phlogopite (Phl), crossed-polarized light; (**c**) anhedral apatite (Ap) crystal included in calcite (Cal). Note the sutured and partly embayed grain boundaries, crossed-polarized light; (**d**) round-shaped pyrite (Py) crystal included in calcite (Cal).
