## 5 Conclusions
The decision rules are: concrete: _Sum_of_abs_\(<\) 10,522; andesite: _Sum_of_abs_\(\geq\) 15,277; granite: (_Count Peaks_10_\(\geq\) 527) \(\cap\) (_Sum_of_abs_\(\leq\) 15,277) \(\cap\) (_Fluctuation_\(\leq\) 132); limonite is the rock that remains after sorting. The measured vibration signal is assumed to be stochastic and stationary. This allows its essential properties and differences during the rock drilling to be characterised with sufficient accuracy even with a sample size of \(n=4500\). The different nature of vibration signals from drilled rocks and concrete is the basis for successful recognition. By this method, the reliability of the classification of three rocks, andesite, granite, limestone, and concrete, is 100%, which is promising. However, it is necessary to mention that the drilling was conducted under laboratory conditions, and all rock and concrete objects were created from a vibration signal for 20 s.  
Given the limited number of samples, possible relationships between differences in the sample values of vibration signal attributes and differences in their petrophysical parameters and petrographic properties will be discussed. Andesite and concrete were easily distinguishable from the other three materials using one vibration signal attribute, _Sum_of_abs_, which represents the sum of all absolute values of the vibration signal amplitudes. For andesite, the classification algorithm defines a lower limit, while for concrete, it defines an upper limit. Concrete differs from all other materials in terms of properties such as compressive strength (lowest of all materials) and grain size (highest of all materials). Andesite differs from granite and limonite in terms of grain size. The grain size for the andesite sample used is very fine-grained, while for granite it is medium- to coarse-grained and for limonite it is fine-grained. Another difference from limonite is its origin. While andesite is an igneous rock, limonite is a sedimentary rock. Andesite and concrete significantly differ from other materials regarding vibration signal attributes such as _Sum_of_abs_, _Sum_o_, _Fluctuation_, _Count Peaks_10_, _Count Peaks_20_, and _Variab_. In addition to the Fluctuation attribute, this difference is visible in Figure 4.  
Creating a set of vibration signal attributes that could correctly classify objects created from the attributes of granite and limestone signals was very difficult. Table 4 shows a significant difference between the averages in the _Sum_of_abs_, _Count Peaks_10_, _Count Peaks_15_, and _Variab_ attributes. However, after creating objects using _Sum_of_abs_, _Count Peaks_10_, _Count Peaks_15_, _Variab_, and _Fluctuation_ attributes, a sorting algorithm was created that correctly classified all granite objects. The sorting procedure is  
as follows and must be followed: (1) (_Count Peaks_10_\(\geq\) 527); (2) (_Sum_of_abs_\(\leq\) 15,277); and (3) (_Fluctuation_\(\leq\) 132). From the perspective of petrophysical parameters and petrographic properties, the difference between them is in their origin. Granite is an igneous rock and limestone is a sedimentary rock. There is little or no difference in compressive strength. However, there is a difference in grain size. Granite is medium- to coarse-grained while limestone is fine-grained. The mineralogical composition of these rocks is not the same. However, the research needs to be supplemented with more rock samples with varying properties, such as travertine, talc, and basalt. In order to use the classification based on the vibration signal in practice, it is necessary to move from laboratory conditions to the field. Adjusting the achieved results by following a similar procedure can yield a method applicable for classification in the field. Further research could analyse the relationships between vibration signal attributes, petrophysical parameters, and petrographic properties of the samples in more detail. Conceptualisation, B.S. and G.B. ; methodology, B.S. and G.B. ; software, B.S. ; validation, P.F. ; formal analysis, G.B. and B.S.