Final answer:
The cleavage or fracture in silicate minerals is influenced by the bonding arrangement of silicon-oxygen tetrahedra, which can be affected by the silicon-to-oxygen ratio and the presence of various cations.
Step-by-step explanation:
Cleavage or fracture in silicate minerals is influenced by the bonding of the silicon-oxygen tetrahedra within the mineral. The arrangement and linking of these tetrahedra vary, from single units to complex frameworks, affecting how the mineral breaks along planes where the chemical bonds are weaker, which are known as cleavage planes.
Specifically, the silicon-to-oxygen ratio plays a significant role due to the fact that silicon-oxygen tetrahedra can exist both as discrete units and in shared corners with other tetrahedra. This structural variability, along with the presence of different cations, results in a myriad of silicate minerals, each with unique cleavage characteristics. For example, amphibole and pyroxene have similar physical properties except for their cleavage angles, which is crucial in discerning between them and understanding the geologic history of the rocks they are found in. Minerals like quartz show no cleavage because of their strong and uniform three-dimensional network of bonds, while mica has perfect cleavage in one direction due to its sheet-like structure.