What Is a Pallasite?
Pallasites belong to the stony-iron meteorite class — a rare group that, as the name suggests, contains both silicate minerals and metallic iron-nickel in significant proportions. Within this class, pallasites are the most abundant type and the most visually striking. Their defining characteristic is a meshwork of iron-nickel metal enclosing rounded to angular crystals of olivine, a magnesium-iron silicate mineral.
When sliced thin and backlit, the olivine crystals — which can range in colour from pale yellow to deep amber and occasionally green — glow with extraordinary translucency. It is no exaggeration to say that a well-prepared pallasite slice is among the most beautiful objects in the natural world.
The Pallas Discovery
The type specimen was found in 1772 near Krasnojarsk, Siberia, by naturalist Peter Simon Pallas — hence the name. Weighing approximately 700 kg in its original mass, it was one of the first meteorites to attract serious scientific attention in the Western world. Pallas's account of the iron-stone mixture initially puzzled scientists who had no framework for understanding extraterrestrial rocks. It was the German physicist Ernst Chladni who later argued, correctly, that such objects must have a cosmic origin.
Where Do Pallasites Come From?
The leading model for pallasite formation places their origin at the core-mantle boundary of differentiated asteroids — bodies large enough to have melted and separated into a metallic iron-nickel core and a silicate rocky mantle early in solar system history.
Under this model, olivine crystals from the base of the mantle became mixed with molten metal from the upper core, then slowly cooled over millions of years as the asteroid's interior solidified. The parent body was subsequently shattered by collisions in the asteroid belt, scattering pallasitic material across heliocentric space. When those fragments eventually cross Earth's orbit and survive atmospheric entry, we recover them as meteorites.
It's worth noting that this model has been debated and refined; some researchers propose impact mixing scenarios or multiple pallasite parent bodies, and the story is not entirely settled.
Types of Pallasites
Meteoriticists recognise several pallasite groupings based on chemistry and mineralogy:
- Main Group Pallasites (MGP) — The most numerous, believed to derive from a single differentiated asteroid parent body. Oxygen isotope and trace element data cluster tightly.
- Eagle Station Pallasites — A small group (three known members) with distinct olivine compositions and different oxygen isotope ratios, indicating a separate parent body.
- Pyroxene Pallasites — An even smaller group containing pyroxene alongside olivine; origin debated.
- Ungrouped Pallasites — Individual specimens that don't fit neatly into any group, suggesting additional parent bodies or unique formation histories.
Notable Pallasite Specimens
Several pallasites are particularly famous within the meteorite community:
- Esquel (Argentina, 1951) — Widely considered the finest pallasite ever found, with exceptionally large, gem-quality, deep golden olivine crystals. Slices are among the most sought-after collector specimens in all of meteoritics.
- Fukang (China, 2000) — Found in the Gobi region, with beautifully transparent olivine and a total known weight of around 1,000 kg, making it the largest modern pallasite discovery.
- Imilac (Chile, 1822) — Recovered in the Atacama Desert; its arid recovery environment preserved specimens in excellent condition.
- Brenham (Kansas, USA) — A Main Group pallasite with a long recovery history; specimens have been found at the site since the 1880s.
Preservation Challenges
Pallasites present unique conservation challenges for collectors. The interface between the metallic matrix and silicate crystals is vulnerable to terrestrial weathering. Moisture causes iron oxidation that can progressively rust and crumble the metal phase, while the olivine can fracture. To preserve slices:
- Store in low-humidity environments, ideally with silica gel desiccant
- Apply a protective coating of museum-grade wax or commercial meteorite sealant
- Avoid direct handling of polished surfaces; oils from skin accelerate corrosion
- Display away from direct sunlight and temperature fluctuations
A well-preserved pallasite slice, cared for properly, can retain its extraordinary appearance for generations — a window into the deep interior of a world that no longer exists.