Identifying high-quality granite requires a comprehensive assessment of multiple aspects, including appearance, physical properties, processing technology, and origin. Here are the specific methods:
1. Appearance Inspection
Color Uniformity: High-quality granite has a uniform color, without noticeable color variations or spots. Lower-quality granite may have varying shades or hues.
Texture Clarity: The pattern is natural and continuous, without breaks or blurring. High-quality granite has a distinctive texture (such as "Brazilian Blue" and "Indian Red").
Surface Gloss: After polishing, high-quality granite has a distinct mirror-like finish, reflecting light evenly; lower-quality granite may appear dull or matte.
2. Physical Property Testing
Hardness and Abrasion Resistance: High-quality granite (Mohs hardness 6-7) should show no scratches when lightly scratched with a key or hard object.
Density and Water Absorption:
A crisp, resonant sound indicates a dense structure.
Water Drop Test: Stone with a low water absorption rate (<0.5%) is more resistant to stains and moisture, and is best if water droplets do not penetrate for an extended period.
Compressive Strength: High-quality granite has high compressive strength (typically ≥100 MPa), making it suitable for load-bearing applications.
3. Processing
Cutting Smoothness: The edges of the slabs should be neat, free of chipping or chipping, and the gaps when splicing should be small and uniform.
Surface Treatment: The polished surface should be free of scratches and pores; the flamed or litchi surface should have uniform grain, free of excessive roughness or damage.
Thickness Standard: Standard slab thickness is ≥1.8 cm (for countertops) or 2 cm (for floors). Thinner slabs are prone to breakage.
4. Common High-Quality Varieties
High-end varieties: Brazilian Blue, New Imperial Red, Norwegian Blue Pearl, and Chinese "Sesame Black."
Mid- to high-end varieties: Shanxi Black, Xinjiang Red, and G603 (Sesame Gray).
5. Avoiding Common Defects
Cracks and Hidden Crevices: Use strong, oblique light to inspect for hidden cracks.
Mineral Impurities: Avoid pyrite (which is prone to rust) or radioactive elements (a test report is required).
Color lines or spots: Large areas of disparate colors may affect aesthetics.
6. Certification and Testing
Radioactive testing: Choose Class A (no radiation hazard, suitable for indoor use) stone and request a test report from the supplier.
Origin and Brand: Stone from well-known production areas (such as Shuitou, Fujian, and Yunfu, Guangdong) or branded stone offers more consistent quality.
7. Recommended Applications
Exterior: Choose dark, high-density varieties (such as "Mongolian Black") for greater weather resistance.
Indoor countertops: Fine-grained, low-water-absorption varieties are recommended (for example, "quartz stone," although manufactured, offers excellent performance).
The above methods can effectively screen for high-quality granite. If your budget allows, we recommend visiting the stone factory to inspect large slabs and requesting small samples for performance testing.