Agate Umbra is known for its beautiful and unique patterns, and it can certainly be used for exterior applications in dusty climates. However, there are a few considerations to keep in mind.

1. Durability: Agate Umbra is a semiprecious stone and tends to be relatively durable. However, its hardness can vary depending on the specific type and quality of the stone. It is important to choose a high-quality agate with good hardness to ensure it can withstand the rigors of an exterior application.

2. Weather Resistance: Agate Umbra should ideally have good weather resistance to withstand dust, wind, rain, and other outdoor elements. However, it is always recommended to consult with the supplier or a stone specialist to confirm its suitability for specific climate and conditions.

3. Sealing and Maintenance: It is advisable to seal agate to provide an added layer of protection against stains, water absorption, and dust accumulation. Regular cleaning and maintenance may be required, especially in dusty environments, to preserve its beauty and prevent any damage.

4. Installation: Proper installation is crucial to ensure the longevity of the stone in exterior applications. It is recommended to hire a professional stone installer who is experienced with working with semiprecious stones and understands the unique requirements of the specific stone.

In summary, while Agate Umbra can be suitable for exterior applications in dusty climates, it is important to consider its durability, weather resistance, sealing, maintenance, and proper installation for optimal performance and longevity. Consulting with stone experts or suppliers can provide more specific and accurate guidance based on your climate and project requirements.