Final answer:
The most important single chain silicate structure among the options is pyroxene. It is characterized by single chains of tetrahedra and distinct 90-degree cleavage.
Step-by-step explanation:
The most important example of a single chain silicate structure among the options listed is pyroxene. In single chain silicates, silicon-oxygen tetrahedra share two oxygens with neighboring tetrahedra to form a chain structure. Pyroxene minerals are characterized by single chains of tetrahedra and have cleavage in two directions at 90 degrees. This differentiates them from amphibole, which forms double chains and has cleavage at 60 and 120 degrees. Other silicates like mica have sheet-like structures, and garnet has an independent tetrahedral structure without sharing oxygens between tetrahedra.