The required load-bearing capacity for a natural marble display rack depends on several factors, including the weight of the marble slabs, the size and thickness of the slabs, and the number of slabs to be displayed. Here are some considerations to help determine the appropriate load-bearing capacity:

1. **Weight of Marble Slabs**: Natural marble slabs can vary significantly in weight depending on factors such as thickness, density, and size. Thicker and larger slabs will typically weigh more than thinner and smaller ones. Obtain the weight specifications for the marble slabs you plan to display to determine the load-bearing requirements.

2. **Number of Slabs**: Consider the number of marble slabs that will be displayed on the rack at any given time. The more slabs there are, the greater the total weight that the display rack will need to support. Calculate the combined weight of all the slabs to determine the load-bearing capacity required.

3. **Distribution of Weight**: Pay attention to how the weight of the marble slabs will be distributed across the display rack. Ensure that the rack is designed to evenly distribute the weight to prevent any single point from bearing excessive load, which could lead to structural failure or damage.

4. **Safety Factors**: Factor in a safety margin or safety factor when determining the load-bearing capacity of the display rack. This helps account for variations in weight distribution, unexpected loading conditions, and potential safety hazards. A safety factor of 1.5 to 2 times the expected load can provide an additional margin of safety.

5. **Rack Material and Construction**: Choose materials and construction methods that can safely support the weight of the marble slabs. Steel, aluminum, and reinforced wood are common materials used for heavy-duty display racks. Ensure that the rack is structurally sound and properly reinforced to withstand the load.

6. **Reinforcement and Support**: Consider additional reinforcement or support features such as cross-bracing, support beams, or adjustable shelves to enhance the stability and load-bearing capacity of the display rack. Reinforce critical areas where stress concentration or bending is likely to occur.

7. **Professional Evaluation**: If in doubt, consult with a structural engineer or a professional specializing in display rack design to assess the load-bearing requirements and ensure that the rack meets safety standards and building codes. They can provide expert advice and recommendations based on the specific requirements of your display setup.

By carefully considering these factors and determining the appropriate load-bearing capacity for your natural marble display rack, you can ensure that the rack safely and securely showcases your marble slabs without risk of damage or structural failure.