## 2 Materials and Methods  
Two slabs of commercial serpentinite were provided by a Spanish stone company (M-12 and M-17, Figure 3). To characterise the stones, we used inductively coupled plasma mass spectrometry (ICP-MS), laser ablation, petrographic microscopes, scanning electron microscopy with energy-dispersive spectrometry (SEM/EDS) and X-ray powder diffractometry (XRPD). After laser ablation, and in order to characterise the obtained powder, we used XRPD, differential scanning calorimetry and thermogravimetric analysis (DSC/TG) and transmis  
Figure 3: Slabs of commercial serpentinite used in our experiments. sion electron microscopy combined with energy-dispersive spectrometry and selected-area electron diffraction (TEM/EDS/SAED). 1. The chemical composition (whole rock major and trace elements) was obtained by means of inductively coupled plasma mass spectrometry (ICP-MS) using an ICP-MS AGILENT 7800. For the analysis, 0.1 g of powder from each sample was digested with HNO\({}_{3}\) + HF under pressure, in high-pressure vessels, in a Milestone microwave. 2. A complete petrographic examination was carried out, following standard ASTM C1721-15 [13], to describe the mineralogy and textures. A Leica DM2500P microscope under transmitted light was used for this purpose. The same microscope was used for the first examination of the powder after laser ablation. 3. X-ray powder diffractometry (XRPD) was used for the characterisation of the samples before (whole rock) and after (filtered particles) laser ablation. XRPD was performed using a Bruker D8 Advance (Bruker, Billerica, MA, USA) X-ray diffractometer at 40 kV and 40 mA. The instrument was equipped with a copper tube and a curved graphite monochromator. Scans were recorded in the range of 3-66 \({}^{\circ}\)20, with a step interval of 0.02 \({}^{\circ}\)20 and a step-counting time of 3 s/step. EVA software (DIFFRACplus EVA) was used to identify the mineral phases and experimental peaks, being compared with the PDF2 reference patterns. 4. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TG) were performed in an alumina crucible under a constant aseptic air flow of 30 mL min\({}^{-1}\) with a Netzsch STA 449 C Jupiter (Netzsch-Geratebau GmbH, Selb, Germany) in a 25-1200 \({}^{\circ}\)C temperature range, with a heating rate of 10 \({}^{\circ}\)C min\({}^{-1}\). Approximately 30 mg of sample was used for each run. Instrumental precision was checked by five repeated collections on a kaolinite reference sample, revealing good reproducibility (instrumental theoretical T precision of \(\pm\)2 \({}^{\circ}\)C), DSC detection limit <1 \(\mu\)W. Derivative thermogravimetry (DTG), derivative differential scanning calorimetry (DDSC), onset and exo- and endo-thermic peaks were obtained using the Netzsch Proteus thermal analysis software (Netzsch-Geratebau GmbH, Selb, Germany). It is worth mentioning that the curve of differential scanning calorimetry (DSC) characterises the heat effects related to the physical and chemical conversion of samples. The thermogravimetric (TG) curve plots the weight variation of the sample during heating; the differential-thermogravimetric (DTG) curve characterises the rate of weight variation in the sample during heating. 5. The morphology of the samples after laser ablation was investigated with a transmission electron microscope (TEM) using a Jeol JEM 1400 Plus (120 kV) equipped with a Jeol large-area silicon drift detector SDD-EDS (Jeol, Tokyo, Japan) for microanalyses. Unambiguous crystallinity of individual fibres was achieved by selected-area electron diffraction (SAED). For TEM investigations, the sample was deposited on a Formvar carbon-coated copper grid. 6. The morphology of the samples before and after laser ablation was investigated via scanning electron microscopy (SEM) using an environmental scanning electron microscope, the FEI QUANTA 200 (FEI, Hillsboro, OR, USA), equipped with an X-ray EDS suite comprising a Si/Li crystal detector model, EDAX-GENESIS 4000 (EDAX, Tokyo, Japan). 7.