Yes, United States Stromatolite Calcarenite can be used outdoors. Stromatolite calcarenite is a type of sedimentary rock that is composed mainly of calcium carbonate and formed by the accumulation of stromatolite fossils. It is a durable and weather-resistant material, making it suitable for outdoor applications such as landscaping, paving, and decorative purposes. However, it is always recommended to consult with a professional or supplier to ensure that the specific type of stone being used is suitable for the intended outdoor use.