Scientists examining lunar soil collected by China’s Chang’e-6 mission have discovered an unexpected form of iron preserved within microscopic impact glass.

Tiny particles of iron trapped inside lunar glass may preserve evidence of the Moon’s ancient magnetic history. Scientists studying soil returned by China’s Chang’e-6 mission have identified face-centered cubic γ-Fe, an unusual form of metallic iron never before confirmed in natural lunar samples.

The discovery is particularly unexpected because γ-Fe normally exists only at high temperatures and changes into a different crystal structure as it cools. Yet researchers found that this phase of iron had survived inside microscopic glass particles formed during impacts on the lunar surface.