Why a rare iron sulfide from space is the gold standard for sulfur isotopes
In short: Troilite is a mineral rarely found on Earth, yet it serves as the international benchmark for measuring sulfur isotopes. While terrestrial sulfur fluctuates due to bacterial activity, troilite from the Canyon Diablo meteorite remains remarkably consistent, providing a stable reference point for scientists studying everything from geology to ancient microbial life.
Troilite is an iron sulfide mineral with the chemical formula FeS. It belongs to the pyrrhotite group, but unlike its iron-deficient cousin pyrrhotite, troilite is stoichiometric and non-magnetic. Its structure is hexagonal, often described as pyrrhotite-2C because its unit cell effectively stacks two basic NiAs-type cells. Though it was first described in 1766 by Domenico Troili in a meteorite that fell in Italy, it was not formally named until 1862, when Gustav Rose recognized its unique composition.
On Earth, troilite is exceptionally rare, appearing only in specific geological settings like layered igneous intrusions in South Africa, Australia, and Greenland. Most troilite found on our planet arrived via meteorites. It is a major component of the Canyon Diablo meteorite, which provides the Canyon Diablo Troilite (CDT) standard. This standard is essential because sulfur isotope ratios on Earth are highly variable, largely due to sulfate-reducing bacteria that process isotopes at different rates. By contrast, meteoritic sulfur maintains a constant isotopic ratio, making it the perfect baseline for comparative analysis.
Beyond Earth, troilite is far more common. It makes up approximately 1% of the lunar crust and is found in all basalt samples returned by the Apollo 11, 12, 15, and 16 missions. It is also a regular feature in Martian meteorites. Theoretical models based on data from the Voyager and Galileo spacecraft suggest that troilite may even be a major constituent of the cores of Jupiter's moons, Ganymede and Callisto, potentially accounting for about 22.5% of their composition.
The mineral's presence is often linked to other metallic ores, including copper, nickel, and platinum. Its rarity in the Earth's crust stands in stark contrast to its ubiquity in the solar system, serving as a reminder that the chemical makeup of our planet is distinct from the extraterrestrial materials that frequently bombard its surface.
Opens the Intellect+ feed with this card first. Swipe up for the next one.
Sources
- Summary by Intellect · source: Troilite
To cite this card, link to https://intellectplus.co.uk/app/nature-troilite.
How we source, check and correct cards: Editorial standards.
General information, not professional advice. Spotted an error? Flag the card or see corrections and complaints.
Intellect Plus is a visual educational discovery platform for exploring fascinating facts and ideas. Brain Food, Not Brain Rot. What is Intellect Plus?
Related
More in Geology · More in Nature · Latest · A–Z · All topics
