I dont have any specific expertise in the grading system for granite stones. However, in general, granite is usually graded based on its quality, durability, aesthetic features, and other characteristics. The grading system may differ from country to country, and there can be variations in the names, grading scale, and criteria for different types of granite.
That being said, China Grey Diamond Granite appears to be a type of granite stone that is commonly found and quarried in China. According to some information sources, this stone is classified as a mid-range or commercial grade granite that is suitable for various applications, such as countertops, flooring, cladding, and landscaping. The color of this stone is mostly grey, with black and white speckles and veins that resemble the texture of a diamond.
In summary, the grade of China Grey Diamond Granite may depend on the specific grading system used by the industry or the supplier. However, based on the available information, this type of granite is generally considered to be a decent quality stone for its intended uses.