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Petrographically, Montescaros marble is dolomitic with crystals visible to the naked eye with coarse equigranular blasts and granoblastic texture. The blasts’ boundaries are very sinuous, and microcrystals fill cracks and blast boundaries (Fig. 6).

Figure 6: Montesclaros marble. a: Altered surface. b: Parallel Nicol microscopic image. c: Crossed Nicol microscopic image.

The porosity is very low. Fig. 7 shows the pore size distribution for the three samples M1 = 0.09 %, M2 = 0.29 %, M3 = 1.46 %.

Figure 7: Montesclaros marble. Pore size distribution determined by MIP for three tested Montesclaros marble samples (M1, M2 and M3).

LMD decresses with the depth. LMD = 17 in the first millimeter and LMD = 9 in the fourth millimeter. The rhombohedral crystals that M4 presents on the surface are due to the alteration, which accentuates the rhombohedral exfoliation, decreasing the equidistance between the microcracks (Fig. 8, red ellipse).

The alteration produces a reduction in the luminosity of the marble. Marble becomes more yellow and red (table 1). The colour difference (ΔE) between dry and wet state has been 18.0, 14.1 and 12.3 for M1, M2 and M3 respectively.

Table 1: Colour parameters of M1, M2 and M3 L*: lightness; a*: red-green value; b*: blue-yellow value.

Dry color
	L*	a*	b*
M1	82.3 ± 1.8	0.7 ± 0.2	4.8 ± 0.6
M2	76.6 ± 1.6	1.9 ± 0.8	8.2 ± 1.5
M3	72.9 ± 1.5	1.9 ± 0.6	8.5 ± 1.4
Wet color
	L*	a*	b*
M1	64.4 ± 15.3	0.8 ± 0.2	6.7 ± 0.6
M2	63.6 ± 2.8	2.9 ± 0.9	13.5 ± 1.6
M3	61.2 ± 2.5	2.2 ± 0.9	12.3 ± 1.9