Collection: Zircon

What are the oldest rocks on Earth, and how did they form? The material that holds the greatest insight into these fundamental questions, because it can contain a record of some of the earliest history of the Earth, is a mineral named zircon. For example, a few grains of zircon found in the early 1990s in a sandstone from western Australia dates back 4.2–4.3 billion years, and we know from meteorites that the Earth is not much older at 4.56 billion years.

Originally formed by crystallization from a magma or in metamorphic rocks, zircons are so durable and resistant to chemical attack that they rarely go away. They may survive many geologic events, which can be recorded in rings of additional zircon that grow around the original crystal like tree rings. Like a tiny time capsule, the zircon records these events, each one of which may last hundreds of millions of years. Meanwhile, the core of the zircon itself remains unchanged, and preserves the chemical characteristics of the rock in which it originally crystallized.