Blaubank Limestone from Germany is a versatile and durable natural stone that can be used for a variety of applications, including exterior ones. However, when it comes to using it in very dusty climates, there are a few factors to consider:

1. Porosity: Limestone is a porous stone, meaning it can absorb moisture and other substances present in the environment. In very dusty climates, the dust particles may settle on the stones surface and potentially seep into its pores. This can result in discoloration and staining over time.

2. Maintenance: To mitigate the effects of dust and maintain the appearance of the limestone, regular cleaning and maintenance will be necessary. The frequency of cleaning will depend on the severity of the dust and the specific conditions of the climate.

3. Finishes: Blaubank Limestone can be found in various finishes, including honed, polished, and natural. A polished finish may be more resistant to dust and easier to clean, but it could also be more prone to showing scratches and wear. A natural or honed finish may be more forgiving in terms of maintenance and may not show dust as easily.

In summary, while Blaubank Limestone can be used in exterior applications in very dusty climates, it will require regular cleaning and maintenance to keep its appearance intact. Additionally, the choice of finish may also impact how prone it is to collecting and showing dust.