The Willamette Meteorite:
The Willamette Meteorite is a rare and important scientific specimen that is preserved as part of the collections of the Museum's Department of Earth and Planetary Sciences. It was found in the Willamette Valley of Oregon and acquired by the Museum in 1906. In structure it is a metallic iron meteorite, weighing over 15.5 tons, the largest meteorite ever found in the United States, and the sixth largest meteorite in the world. Metallic iron meteorites are a relatively rare kind of meteorite. They comprise a class of about 600 out of a total of 25,000 meteorites so far found on the Earth's surface.

The microscopic structure of the meteorite is unusually complicated and suggests a unique set of events subsequent to its original formation, yet to be fully analyzed. What we do know about formation of the Willamette Meteorite can be best summarized in four stages.

Stage 1: Billions of years ago in the early history of our solar system, a planet which orbited the Sun was shattered. Fragments of this shattered planet likely included the Willamette Meteorite, which probably represents the iron-nickel core of this planet. The original break-up of the planet and cooling of the resulting fragments is evident in the microscopic structure of the meteorite.

Stage 2: During its long sojourn in space, the Willamette Meteorite sustained at least two subsequent shocks. These were high-energy impacts likely due to collisions among planetary fragments, which caused re-heating and re-crystallization observable in the micro-structure of the meteorite. One of these shocks may have been responsible for knocking the Willamette Meteorite into a collision course with the Earth.

Stage 3: Perhaps a billion years later, the meteorite penetrated the Earth's atmosphere and collided with the Earth's surface at supersonic speed. Unfortunately, we cannot directly see any remnants of this impact stage because of long-term weathering of the meteorite after its impact.

Stage 4: The final form of the Willamette Meteorite resulted from the long-term exposure and weathering in the humid Northwest region. The large cavities on the exposed flat side of the meteorite formed not in space but on Earth during this weathering period. This occurred from interaction of rainwater with iron sulfide deposits in the meteorite, producing weak sulfuric acid. The etching by this acid, an extremely slow process, dissolved the metal and produced the cavities that you see now.