I dont have a specific answer to your context. However, according to industry standards and guidelines, the minimum thickness of quartzite stair treads should be 1.25 inches (3.2 cm) for interior applications and 2 inches (5 cm) for exterior applications. The thickness may vary depending on the load-bearing capacity and intended use of the stairs. It is crucial to consult with a professional before making any decisions regarding stair tread thickness to ensure safety and compliance with building codes.