**2. Materials and Methods**

#### *2.1. Sampling*

Marble samples were collected from the interior facings of the Holy Aedicule (Chapel of the Angel and Holy Tomb Chamber), as well as from the marble slabs enclosing the Tomb of Christ. Six marble samples were studied: four from the Holy Tomb Chamber and two from the Chapel of the Angel. In particular, in the Holy Tomb Chamber, one sample was taken from the marble facing of the interior south wall opposite the Tomb, while the other three were collected from the Holy Tomb cladding: one from the upper marble plate, worshipped today, one from the interior marble plate, which was revealed during the NTUA rehabilitation project, and one from a marble fragment found within the Tomb. Two marble samples were collected from the western wall of the Chapel of the Angel, northern and southern to the low entrance of the Holy Tomb Chamber, respectively.

A summarized description of the marble samples under investigation and their sampling location is presented in Table 2. Sampling locations on the ground plan of the Holy Aedicule are presented in Figure 5, while in Figures 6–9, views of the sampling areas are displayed.



\* The amber hued coloration is noticed on the external surface of the marble plate and it is attributed to the application of myrrh for centuries as part of the liturgical functions.

**Figure 5.** (**a**) Depiction of sampling locations on ground plan of the Holy Aedicule (ground plan modified from Lampropoulos et al 2017 [70]); (**b**) View of the Holy Tomb from the entrance on the east; (**c**) Schematic representation of the Holy Tomb: section depicting the layering of materials and the sampling areas of OM11, OM49, OM10.

**Figure 6.** Description of sampling areas of marble samples (1) OM10 and (3) OM11: (**a**) the Holy Tomb with the top amber hued marble plate, that it is worshiped today, in place; (**b**) View of the Holy Tomb during the shifting out of position of the top amber hued marble plate on October 26, 2016; (**c**) The open Holy Tomb where it was visible: the Holy Burial Bed Rock; the fragmented gray marble plate (sampling area of (1) OM10); the, shifted out of position, top amber hued marble plate (sampling area of (3) OM11).

**Figure 7.** Sample (2) OM49: the marble fragment, found within the Holy Tomb; (**a**) front view, where characteristic grey stripes can be macroscopically observed; (**b**) top view, where mortar residues are evident; (**c**) side view, where mortar residues and a special curved ending are evident; (**d**) the other side view, where, besides the special curved ending, characteristic grey stripes can be macroscopically observed.

**Figure 8.** Description of sampling area of marble sample (4) OM13: smooth interior marble facing, opposite the Holy Tomb in the Holy Tomb Chamber.

**Figure 9.** Description of sampling areas of marble samples (5) OM50 and (6) OM51 in the Chapel of the Angel; At the right hand side-northern to the Tomb Chamber entrance, the sampling area of sample (5) OM50, is displayed; At the left hand side-southern to the Tomb Chamber entrance, the sampling area of sample (6) OM51, is displayed.

#### *2.2. Analytical Techniques*

From the six (6) marble samples that were collected, thin-and-polished sections were created and underwent detailed petrographic investigation. The technique of optical microscopy was performed using a Leica DM2500P optical microscope mounted with a Nikon camera. MGS values were measured on images collected through a ProgRes-C14PLUS video-camera, using the ProgRes CapturePRO2.1 software.

Stable isotope (C, O) analyses of the studied marble samples were performed; marble chips, hand-picked for every sample under the stereoscope in order to avoid any contaminations of the samples (e.g., from mortar rests), were pulverized in an agate mill for this purpose. The marble powders were reacted with 100% phosphoric acid at 70◦C using a Gasbench II connected to a ThermoFisher Delta V Plus Mass spectrometer. All values are reported in per mil relative to V-PDB (Vienna Pee Dee Belemnite). Reproducibility and accuracy were monitored by replicate analysis of laboratory standards calibrated by assigning <sup>δ</sup>13C values of +1.95‰ to NBS19 and <sup>−</sup>47.3‰ to IAEA-CO9 and <sup>δ</sup>18O values of <sup>−</sup>2.20‰ to NBS19 and <sup>−</sup>23.2‰ to NBS18. Reproducibility for <sup>δ</sup>13C and <sup>δ</sup><sup>18</sup> O was <sup>±</sup>0.01 and ±0.08, respectively.

#### **3. Results**

#### *3.1. Petrographic Characterization of the Studied Samples*

The studied samples were taken from an archaeological monument of great significance, thus each one will be described separately in the present section. Panoramic microphotographs, taken under crossed-polarized light are presented in Figure 10. Detailed textural and petrographic characteristics for each sample are depicted in Figures 11–16.

**Figure 10.** Transmitted light, panoramic microphotographs of the studied samples, taken under crossed-polarized light: (**a**) Sample OM10; (**b**) sample OM11, (**c**) sample OM13; (**d**) sample OM49, note the mortar rest on the right corner of the sample; (**e**) sample OM 50; (**f**) sample OM51. Note the characteristic heteroblastic fabric on all samples (mortar-type). Red dotted lines mark the areas that belong to grey-colored bands in samples OM10 and OM49.

A common characteristic of all six samples is that they emit an intense smell of sulfur upon scraping or hitting, fact that implies an organic component (bituminous compounds). Coloration of the studied samples is relatively homogeneous, around 180–200. Two of the samples (OM10 and OM49) are characterized by a relatively small number of parallel and mm-sized grayish bands that can be observed even in macroscopic scale. In microscopic scale, these bands are composed of fine-grained calcite, indication that the rock has suffered an extent of tectonic deformation. What is also common in all the studied samples is their characteristic heteroblastic fabric, known as "mortar-type". This fabric is characterized by two groups of crystal sizes: the first largest group comprises subhedral calcite porphyroblasts, which maximum grain size (MGS) ranging from 1.6 up to ~3 mm (most common values are >2 mm). This fact is helpful to characterize the studied samples as medium/coarse grained marbles, as the value of 2 mm is commonly used in archaeometry as a cutoff between the fine- and medium/coarse-grained marble varieties [3]. The second group is characterized by much smaller MGS (less than 1 mm). These grain sizes are detected in the Holy Aedicule samples under examination, in the grey-colored bands of samples OM10 and OM49, as well as in calcite crystals that form around the porphyroblasts, due to strain deformation and subsequent neocrystallization. Deformation of the rocks is also evidenced by bent twinning lines in calcite crystals. Accessory minerals in all samples include mainly mica (phlogopite), while minor apatite and pyrite were also observed. Dolomite was also identified, but its volumetric participation in the rocks is rather insignificant.

**Figure 11.** Transmitted (**a**–**c**) and reflected (**d**) light microphotographs of sample OM10: (**a**) Heteroblastic fabric ("mortar"), crossed-polarized light; (**b**) sutured and partly embayed grain boundaries, crossed-polarized light; (**c**) anhedral apatite (Ap) crystal included, along with phlogopite (Phl) in calcite (Cal), plane-polarized light; (**d**) round-shaped pyrite (Py) crystals included in calcite (Cal).
