Sunstones: The Good, The Bad, & The Ugly (in other words, the complex petrogenesis of our state gemstone)

Emily Cahoon

Oregon State University

Watch the recorded presentation

5:30 pm social hour

6:00 pm student poster session

7:00 pm presentation

Sunstones are copper-bearing and gem-quality plagioclase crystals found within basaltic lavas in eastern Oregon. Native copper is visible as macroscopic platelets within the crystals and evidence suggests it partitioned magmatically into the crystal structure during growth. Lava flows containing sunstones are situated within the spatial footprint of the Columbia River Basalt Group (CRBG), the worlds youngest continental flood basalt. This has led to the assumption that sunstones are petrogenetically linked to the CRBG, as nearby CRBG lavas often contain coarse plagioclase phenocrysts. This connection however is unconfirmed, and ages for sunstones and hosting basaltic groundmass indicate they were emplaced during two temporally discrete eruptive events. In this talk, we explore the eruptive timing, spatial distribution, and geochemical homogeneity of these copper-bearing plagioclase crystals -- giving insights on the magmatic plumbing systems and melt segregation processes within flood basalt provinces. Dr. Emily Cahoon will also highlight aspects of these ethically sourced gemstones and the copper inclusions that make them unique.

Oregon State University student poster session at 6:00 pm:

Join us before the talk for a student poster session from three OSU students working with Dr. Emily Cahoon on various aspects of sunstone research. Each of these students was a recipient of a 2023 COGS student research grant.

Kyle Nunley: Argon geochronology on basalt and hosted sunstones in eastern Oregon

Scott Toney: Sunstones: A gemstone formed by a magmatic or hydrothermal process?

Cheyenne Yost: Copper and lithium diffusion analysis of eastern Oregon sunstones

Please join us at Bridge 99 Brewery:

63063 Layton Avenue, Bend

5:30 pm social hour

6:00 pm student poster session

7:00 pm presentation

COGS talk are free and open to the public -- all are welcome! Please join us for the social hour before the presentation.

All presentations are also live-streamed through Zoom. There will be a registration link at the top of this page as we get closer to the date of this presentation.