I dont have access to information about grades of natural stone in Brazil. However, in general, the grade of a stone is determined by its color, pattern, texture, and other characteristics, in relation to its intended use. Quartzite is a hard and durable natural stone that is often used for countertops, wall cladding, and flooring in high-end residential and commercial projects. It comes in various grades, from premium to commercial, depending on the quality of the material and its surface finish. The grading system may vary depending on the country of origin and the supplier, but it typically involves a set of criteria that assess the stones color consistency, veining, thickness, size, shape, and defects, such as pits, cracks, or fissures. Ultimately, the grade of a stone is a subjective judgment that involves the buyers and the installers expectations and preferences.