## 5 Discussion  
The ultramafic rocks presented in this study underwent variable serpentinization degrees as indicated through the petrographic and geochemical analysis outlined above. Dominant parameter for physico-mechanical and physico-chemical properties from two different complexes presented is the degree of serpentinization. Serpentinization oftentimes takes place under ocean floor formation environment [31]. This environment aids the transformation of primary Mg-rich silicate minerals (e.g., olivine and pyroxene) into secondary phyllosilicate phases, belonging to the serpentine group minerals; their prominent features are their softness and flakiness [35; 36]. Various studies have demonstrated the effect of serpentine formation upon rocks' engineering properties [16; 17; 18; 73]. These are greatly undermined due to the alteration of the primary and harder minerals into the much softer and less compact serpentine, resulting into lithotypes mechanically unstable under stress and thus limiting their range of uses [12]. Additionally, serpentinization is a complex process which modifies the textural, and physical properties as well as their geochemistry and has been investigated by several researchers [74; 75]. Serpentinites can be formed in a plethora of tectonic settings. Several factors such as the composition of water, the tectonic activity of rocks and the type of geotectonic environments are responsible for serpentine formation [32; 75]. Subducted sediments along with oceanic crust experience dehydration; the produced fluids interact with both the subducted serpentinite and mantle periodtites, which become progressively hydrated. This results in an active subduction zone [76], whereas a second-stage serpentinization, related to faults when the slab bends near the trench [77]. Faults and especially normal faults act as channel-carrying dehydration fluids which interact with the subducted peridotites and create serpentinites. On the other hand, in fast-spreading ridges, major magmatic activity usually occurs, being responsible for the development of a thick oceanic crust so abyssal periodites cannot outcrop on the seafloor [78], preventing further alteration. There are chemical indices regarding the ultramafic rocks which may determine their properties. In this context, we introduce the term 'fertility rate' (FR) that relies on selected primitive mantle normalized [79] major and trace element abundances deemed as petrogenetically critical for characterization of ultramafic rocks as fertile through the following equation:  
\[ \begin{split}\text{F.R.}=[\text{TiO}_{2}(\text{wt.%})/0.201+\text{ Al}_{2}\text{O}_{3}(\text{wt.%})/4.45+\text{CaO}(\text{wt.%})/3.55+\text{Y}(\text{ppm})/4.3\\ +\text{Yb}(\text{ppm})/0.441+\text{Dy}(\text{ppm})/0.674\text{l} /\text{n},\end{split}  \tag{1}\]  
where n: number of participating element ratios in the equation. The primitive mantle normalized values of each participating element in the equation above have been divided into the factor \"n\", which is equivalent to the value of \"6\" if all of the aforementioned measured elements are above their detection limits. Thus, an \"ideal\" primitive mantle lherzolite should obtain the FR value of \"1\". Based on this, FR valuesranging between 1.00 and 0.90 correspond to highly fertile ultramafic rock, between 0.90 and 0.70 to fertile ultramafics, between 0.70 and 0.50 to moderately depleted, between 0.50 and 0.20 to depleted and <0.20 to highly depleted harzburgites. The aforementioned major and trace elements are commonly enriched in fertile Iberzolite mantle sources relatively to harzburgite counterparts [80; 81]. The F.R. is highly correlated with the mineralogical assemblage, being enriched in the main REE and trace element carriers, i.e., clinopyroxene and in lesser amounts plagioclase [82; 83; 84], in which relatively high values point to mantle sources associated with a MORB-related geotectonic environment.