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# A Diamond Swallowed a Speck of Seafloor. Then It Came Back Up.
- URL: https://www.gottabekidding.me/a-diamond-swallowed-a-speck-of-seafloor-then-it-came-back-up/
- Published: 2026-09-29T10:04:00.000Z
- Updated: 2026-09-29T10:03:59.000Z
- Description: Geologists usually toss out this kind of mineral pocket as contamination. This one was sealed tight, and it may explain where some of the ocean's water ends up.
- Author: Groundwater
- Tags: Earth Sciences

A super-deep diamond from Brazil was carrying a speck of something that belongs in a garden. Sealed inside was goethite, the iron mineral that turns soil brown, alongside hematite and magnetite, two more minerals common in soils and on the ocean floor.

That's a strange thing to find in a stone from this deep. Most diamonds form about 150 kilometers (93 miles) down; super-deep ones form below 300 kilometers (186 miles). Iron minerals like these usually get written off as contamination that seeped in through a crack. But X-ray scans showed this pocket, inside a diamond just 3 millimeters (about 0.1 inch) long, had no connection to the outside world.

Goethite wasn't supposed to make that trip. It forms where iron-rich minerals meet water, and it locks some of that water into its crystal structure. When an ocean plate sinks into the mantle, temperatures above 200 C (392 F) were thought to break goethite down early in the descent. And yet here it is.

The team suggests goethite can survive the ride tucked into cool, deep cracks in a sinking plate, then release its water far below, possibly as deep as the lower mantle, which starts about 660 kilometers (410 miles) beneath the surface. Not everyone is convinced. The lab evidence the team leans on is disputed, and other experiments suggest goethite gives up its water much shallower.

The mantle may be wetter than we thought. The diamond is not taking questions.

**Read the full story at** [Agência FAPESP, July 29, 2026](https://agencia.fapesp.br/analysis-of-a-super-deep-diamond-reveals-how-water-travels-to-the-earths-interior/58806?ref=gottabekidding.me)

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**Hot Take:** Geologists thought they were looking at a composter. This diamond makes subduction look suspiciously like a freight elevator.