**Giovanni Martinelli 1,2,3,\*, Paolo Plescia 4, Emanuela Tempesta 4, Enrico Paris <sup>5</sup> and Francesco Gallucci <sup>5</sup>**


Received: 18 July 2020; Accepted: 29 September 2020; Published: 30 September 2020

**Abstract:** This study assesses the correlations between the intensity of stress undergone by crystals and the morphological characteristics of particles and fracturing products. The effects of the fractures on the microstructure of quartz are also studied. Alpha quartz, subjected to shear stress, is quickly crushed according to a fracturing sequence, with a total fracture length that is correlated to the stress rate. The shear stress generates a sequence of macro and microstructural events, in particular localized melting phenomena, never highlighted before on quartz and the formation of different polymorphs, such as cristobalite and tridymite together with amorphous silica.

**Keywords:** quartz; shear stress; tribochemistry; fracturing
