## 1 Introduction  
### The Marble Industry Context  
Marble is highly used as a building material in construction due to its aesthetics, durability, and long-lasting characteristics [1, 2, 3]. Usually, marble slabs last as long as the buildings in which they were incorporated. This characteristic has motivated an increasingly high demand for this resource world-wide followed by a growing production quantity, reaching more than 150 million tons of ornamental natural rock in 2019 according to [4]. This means that the marble industry plays an important role in the economic structure of many countries. A considerable part of the quarrying and processing activities, in this industry, are performed worldwide by small and family-owned companies, which have a limited financial budget for investing in new techniques and machinery. This financial constraint leads to the use of less efficient methods, generating high production costs and significant waste of raw material. The most common method used to process marble goods starts with the quarrying of large marble blocks, which according to [5] are separated from the rock face by means of straddle bearing or explosions. Then, smaller portions are cut from the main block, using traditional cutting techniques, involving diamond wire saws that make linear cuts in the rock. The newly cut slices undergo a second stage of processing in which the blocks are separated by their geometric characteristics, external appearance, and cut into smaller slabs and tiles. The final stage involves polishing treatments and preparation for commercial use. This complete production process originates a considerable amount of waste in all stages: (i) in the quarrying stage; according to [4], in 2019 worldwide, about 50% of the total gross quarrying was wasted and; (ii) in the processing stage, more than 40% went to waste. Most part of the quarrying waste is produced when the block is removed from the rock face, since it is very hard to completely control the explosion, and most of the times a lot of debris is produced. In the processing stage, the wasted material comes from different sources (sawing sludge, stone fragments, cracked marble blocks without sufficient structural integrity, insufficient appearance specifications, due to color, number of veins, etc.). In the processing stage, the most significant waste is mainly due to the unknown inner structure of the marble block until the actual cut is done. Nowadays, the inner shape and viability of a stone block is empirically assessed based on the skill and experience of the employees, who make predictions based on external observation. To follow this procedure is clearly a high risk, and it is urgent to find a better and more sustainable procedure, as the stone industry influences significantly the landscape. This paper aims to present an alternative procedure based on facts rather than intuition. This new approach aims to reduce the waste generated in the processing stage and therefore optimize the output of the stone blocks. This objective can be accomplished by approaching two problems: (i) avoid the effort expended in cutting unviable blocks (absence of structural integrity, existence of unacceptable vein patterns); (ii) predicting in advance the surface quality of the slabs, still before processing the stone block (allows a significant improvement on customer satisfaction). In addition to these two significant improvements, the stone manufacturing company leverages its economic value by advertising digital-twins of the tiles that a block can produce, pricing the different blocks according to their internal structure (quality of the cut slices), with different price tags, allowing customers to preview the finished product before cutting the stone blocks. To be able to achieve all these goals, a method of predicting the interior structure of a stone block must be created. At present, researchers are committed to developing mathematical models to predict the internal structure of stone blocks based on non-destructive tests made on the blocks.