3.1.3. Sample OM13

Calcite is the dominant mineral component of the sample. Dolomite is present in minor amounts. The sample exhibits a heteroblastic fabric ("mortar-type", Figure 13a,c), with maximum grain sizes being slightly smaller compared to the other samples, around 1.6mm. Deformation is also remarked in this sample, as xenomorphic crystals of calcite in the groundmass often exhibit polysynthetic twinning. Rarely, triple point junctions of calcite grains (Figure 13b) were observed. Micas (phlogopite muscovite), anhedral apatite and round-shaped pyrite were identified as main accessory phases (Figure 13c,d).

**Figure 13.** Transmitted (**a**–**c**) and reflected (**d**) light microphotographs of sample OM13: (**a**) Heteroblastic fabric ("mortar"), crossed polarized light; (**b**) slightly sutured calcite (Cal) grains forming triple-point junctions, plane-polarized light; (**c**) anhedral apatite (Ap) crystal included in calcite (Cal). At places calcite includes phlogopite (Phl). Note the sutured and partly embayed grain boudaries; (**d**) round-shaped pyrite (Py) crystal included in calcite (Cal).
