# Properties of the Ignimbrites in the Architecture of the Historical Center of Arequipa, Peru
## 2 Materials and Methods  
Eight prismatic specimens measuring 40 \(\times\) 40 \(\times\) 160 mm\({}^{3}\) and 24 cubic specimens with a 50 mm edge were prepared from the samples of white ignimbrite from the Afhashuayco quarry (Wt samples) and beige ignimbrite from the La Estrella quarry in the area furthest from the volcano (Be samples). Only six cubic samples of pink ignimbrite (Pk samples of Uchumayo) were used, due to limited availability (Figure 2a).  
Petrographic characterization through optical polarized microscopy (OM) was performed using a Carl Zeiss Jena AMPLIVAL Pol-U. For the morphological determination, scanning electronic microscopy (SEM) was required, using JEOL JSM 5400 and a magnification range from 15X to 200,000X in both backscattered electron (BSE) and secondary electron (SSE) mode with a ZEISS DSM 94 supported by EDX Oxford ISIS-Link; X-ray diffraction (XRD) with powder diffractometer Bruker D8 Advance used the DIFFRACplus software.  
The preliminary chemical quantification required portable X-ray fluorescence equipment: Thermo Scientific Niton XL3t 980 with a geometrically optimized large area drift detector (GOLDD+) energy-dispersive XRF (EDXRF). The analyzer works up to 50 kV  
Figure 2: (a) Location. (b) Western front of Afhashuayco quarry (Chachani volcano to the right).  
and 40 \(\upmu\)A. The calculation of elemental concentrations was made from the \"Test All Geo\" integrated algorithm specific for stone materials.  
In addition, the Na\({}^{\pm}\), K\({}^{\pm}\), Ca\({}^{2\pm}\) and Fe\({}^{2+}\) concentrations were measured by inductively coupled plasma atomic emission spectrometry (ICP-MS, Iris Advantage, Thermo Fisher Scientific). The analysis was conducted through three measurements of each solution.  
The porous network distribution [15] was assessed, using Mercury Porosimetry (Micromeritics Autopore IV 9500), with detection ranges (at 414 MPa) between 0.005 \(\upmu\)m and 360 \(\upmu\)m, i.e., those pore accesses that are smaller than 360 \(\upmu\)m.  
Apparent density, water absorption at atmospheric pressure and the water absorption coefficient by capillarity measurements were determined following standards UNE-EN 1936, UNE-EN 13755 and UNE-EN 1925, respectively. Mechanical characterization, such as flexural strength under concentrated load and uniaxial compressive strength, were estimated following standards UNE-EN 12372 and UNE-EN 1926, respectively. The ultrasound pulse velocity (m/s) was measured using Pundit Plus with frequency transducers of 54 MHz. The anisotropy index (AD) for capillary water uptake and ultrasound velocity was calculated following [PERSON] et al. [16] based on the ratio between the minimum and maximum values for each sample.  
Surface hardness was measured using a Leeb tester KH-100, which is a dynamic method relating the rebound (Rp) and the impact velocity (lp) of 75 g (type D impact device) with a result on the Leeb scale (HL\({}_{\text{D}}\) = 1000 Rp/lp \(\times\) 1000). Considering Leeb rebound hardness (LRH), it is more accurate, compared to Shore hardness tests [17].  
The color was quantified using a Minolta CR-200 (D65 illuminant, with a diffuse beam of 8 mm in diameter, a viewing angle geometry \(\theta\)[18]. It was measured using the CIE L* a* b* system. The parameter L*, or luminosity, records the values from 0 (black) to 100 (white); a* and b* are the color indices given in Cartesian coordinates (a* ranging from \(-60\) (green) to +60 (red) and b * ranging from \(-60\) (blue) to +60 (yellow), respectively). Given the textural heterogeneity, 100 measurements were taken for each stone type. The total color variation (\(\Delta\)E*), particularly significant between white and beige ignimbrites, was calculated as follows:  
\[\Delta\text{E*}=[(\Delta\text{L*})^{2}+(\Delta\text{a*})^{2}+(\Delta\text{b*} )^{2}]^{\tfrac{1}{2}} \tag{1}\]  
The parameter \(\Delta\)E* indicates the total color variation with a threshold of perception of the color difference for the human eye with values greater than \(\Delta\)E* = 3 [19].