1：Experimental Design and Method Selection:

The study combined results from an internationally recognized test for measurement of rock deformation/strength and the concurrent measurement of NIR spectra using a conventional spectrometer. The rock test chosen was a modified version of the internationally accepted method to determine the tensile strength of rocks, the Indirect Brazilian Tensile Test (IBT).

2：Sample Selection and Data Sources:

Four samples of three different rock types were used to represent a broad range of geological materials; an orange, granular sedimentary Darley Dale sandstone; a crystalline metamorphic yellowish white Bianco Carrara marble, and a dark grey, crystalline igneous Basalt taken from Mt Etna, Sicily.

3：List of Experimental Equipment and Materials:

Samples were mounted in a standard tensile curved-jaw loading jig and force was applied using an Instron 600LX load frame and data logger. Spectra were captured using an analytical spectral devices (ASDs) Labspec 5000 spectrometer.

4：Experimental Procedures and Operational Workflow:

The sample was in contact with the rig only at the top and bottom of the specimen so that the sides of the sample were unrestrained. A vertical load was applied and increased at a strain rate of 5 × 10?5 s?1 until the rock sample failed due to lateral (tensile) expansion.

5：Data Analysis Methods:

Reflectance spectra of each rock type were analysed to identify a common wavelength or group of wavelengths that showed consistent variation with increasing strain. Regressions between strain and reflectance at specific wavelengths were carried out to determine a statistical relationship.