Through the Lens

Like stained glass in a historic cathedral window, this luminous, 1-milimeter zircon crystal glows in cross-polarized light. Formed in molten magma about 2 billion years ago, the crystal was eroded, transported and deposited in a river in southern Minnesota about 1.7 billion years ago. The crystal — encased in deep red and black hematite and glassy gray quartz — shows delicate growth lines from its time inside the magma. Zircon crystals contain radioactive uranium, which slowly decays to stable lead. For this reason, zircon is used to determine the age of the most ancient rocks on earth.

Photo by Eric Hiatt, UW Oshkosh associate geology professor, as part of his research on early earth environments.