The load-bearing capacity of display racks for marble depends on various factors including the weight of the marble pieces, the size and dimensions of the display rack, and the materials used in its construction. Here are some general guidelines:

1. **Weight of Marble**: Determine the average weight of the marble pieces you intend to display. Marble can vary significantly in weight depending on factors such as thickness and size.

2. **Design and Construction**: Choose display racks that are specifically designed to support heavy items like marble. Look for racks made from sturdy materials such as steel or reinforced wood.

3. **Load Rating**: Check the load rating or weight capacity of the display racks. This information is usually provided by the manufacturer and indicates the maximum weight that the rack can safely support.

4. **Distribution of Weight**: Consider how the weight of the marble will be distributed across the display rack. Ensure that the rack is designed to evenly distribute the weight to prevent any weak points or instability.

5. **Safety Factors**: It's advisable to err on the side of caution and choose display racks with a higher load-bearing capacity than strictly necessary. This provides a safety margin and reduces the risk of overloading the racks.

6. **Consultation**: If you're unsure about the appropriate load-bearing capacity for your specific needs, consider consulting with a professional such as an engineer or a manufacturer specializing in display racks for heavy items like marble.

By considering these factors and choosing display racks with sufficient load-bearing capacity, you can ensure safe and secure display of marble products in your exhibition or showroom.