Acasta Gneiss

Acasta Gneiss is an ancient rock formation in the Northwest Territories composed of different types of gneiss alongside mafic and ultramafic rocks. It spreads across a large area southeast of Great Bear Lake in the Canadian Shield region.

The formation was discovered in 1983 by geologist Janet King and named after the nearby Acasta River during a mapping program. This find made it a key reference point for understanding Earth's early history.

Scientists worldwide reference the Acasta Gneiss when studying Earth's early geological processes, making it a cornerstone of planetary research and education.

The remote location southeast of Great Bear Lake is only accessible by aircraft, limiting visits to specialized research expeditions. Preparation for arctic conditions is essential for anyone wanting to explore this region.

Zircons within the formation have been dated to roughly 4 billion years old, making it Earth's oldest known rock formation. This age provides unique insight into how the early planet was composed and evolved.

Location: Northwest Territories

Made from material: gneiss

GPS coordinates: 65.16660,-115.58200

Latest update: December 6, 2025 22:09