Silification Geology (OPALS) with Patrice Rey

September 30, 2026

AI Summary

5 min read

In 1993, Australia declared the opal its national gemstone, and a French-born geophysicist named Patrice Rey felt an odd sense of obligation. He had been obsessed with opals since watching a documentary about Australian miners as a ten-year-old boy in France. Decades later, after a random phone call from the Lightning Ridge Opal Miners Association pulled him into the field, Rey cracked the geological code of how these rainbow stones form—and found a surprising link to Mars.

What Makes an Opal an Opal

Most precious gemstones—diamonds, rubies, sapphires—are crystalline. They form deep underground under extreme heat and pressure. Opals are not crystals at all. They are amorphous, made of silica dioxide (the same stuff as sand and quartz) plus about ten percent water. They form not in the deep crust but close to the Earth's surface, in a watery gel.

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What you'll learn

1 (00:19) **What Are Opals & Why Are They Weird?** - Alie Ward introduces the topic of opals and the episode's guest, geoscientist Patrice Rey.
2 (04:14) **Childhood Dream & The Call to Opals** - Patrice Rey recounts his childhood inspiration from a documentary on opal mining and his eventual path to studying them.
3 (10:53) **Where Opals Are Found & The Opal Rush** - Discussion on the global distribution of opals, the history of the Australian opal rush, and the difference between precious and potch opal.
4 (15:25) **How Opals Form: The Silica Gel & Spheres** - Patrice explains the unique, non-crystalline formation of opals from a silica gel and the crucial role of silica spheres.
5 (18:03) **Opals' Water Content & Shallow Formation** - The episode contrasts opals with other gemstones, highlighting their high water content and formation near the Earth's surface.
6 (21:15) **Black Opals & The Smelly Swamp Origin** - Patrice describes the formation of black opals from organic matter in ancient, stagnant swamps.
7 (24:26) **Synthetic vs. Simulated Opals** - A breakdown of the differences between natural, synthetic, and simulated opals, including the story of a creationist miner.

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Show Notes

Gems of lightning and shadows. Rainbow fossils. Underground tunnel homes. Mysterious sedimentary origins. Aboriginal dreamtime stories. Armored snails. Questionable song lyrics. It’s opals, folks. And world expert geophysicist and University of Sydney professor Dr. Patrice Rey is here to talk about why he left France to explore the geological mysteries of the Outback. Should you get an opal engagement ring? Can they get wet? What’s the difference between an Australian and Ethiopian opal? What was one doing in a Kenyan cave 3000 years ago? What’s a Kyoto Opal vs. opalite? And why was your great grandma named Opal?

(Cultural warning to Aboriginal and Torres Strait Islander listeners: this episode mentions names and stories of people who have passed.)

Visit Dr. Rey’s website and follow him on Google Scholar

A donation went to the GO Foundation