Reasons:

* Chemical Composition: Marble is primarily composed of calcium carbonate (CaCO3), which is susceptible to chemical weathering by acidic rain and other acidic substances. Granite, on the other hand, is composed of quartz, feldspar, and mica, which are more resistant to chemical weathering.

* Porosity: Marble has a higher porosity than granite, meaning it has more pores and spaces that can absorb water. This makes it more vulnerable to freeze-thaw cycles and chemical weathering.

* Mineral Content: Marble contains minerals like calcite, which are easily dissolved by acidic solutions. Granite contains minerals like quartz, which are more resistant to dissolution.

Weathering Processes:

* Chemical Weathering: Marble reacts with acidic substances, leading to the formation of soluble salts. These salts are then removed by rain or groundwater, causing the marble to dissolve and erode.

* Physical Weathering: The higher porosity of marble makes it susceptible to frost wedging, where water freezes and expands in the pores, causing the rock to break apart.

Examples:

* The Taj Mahal in India, made of white marble, has been significantly weathered by air pollution and acidic rain.

* Granite monuments, such as the Washington Monument in Washington, D.C., are known for their durability and resistance to weathering.

Conclusion:

Due to its chemical composition, porosity, and mineral content, marble weathers faster than granite. This difference in weathering rates can be observed in the appearance of marble and granite structures over time.