Yes, New Zealands Pennyweight Schist can be used for exterior applications in very rainy climates. Schist is a durable and weather-resistant natural stone that is commonly used in construction and landscaping projects. It has excellent water resistance properties and can withstand heavy rainfall without experiencing significant deterioration or damage. However, proper installation techniques, including the use of appropriate sealants and drainage systems, should still be followed to ensure the longevity and durability of the stone in such climates.