It’s common for researchers to conduct a mineral analysis on a suspected meteorite, dissecting and identifying its compounds to determine what it is and where it came from. The process is usually done with ease, and generally gives researchers a simple method for establishing origin. But that simplicity was challenged when researchers came across a peculiar pebble in southwest Egypt, with a mineral makeup unlike any other planetary object.

Unlike most meteorites, which have chemical compositions similar to Earth and the other rocky planets, this one had elements in the wrong proportions, or in forms not usually seen in the inner solar system. It raises the question: Is our idea of how the solar system formed and how the elements were originally scattered throughout it the right one?

A rock of unusual composition

The curious case started in 2013 when a team of researchers at the University of Johannesburg revealed that an Egyptian stone, discovered in 1996, was definitely extraterrestrial. In 2015, a separate group of researchers conducted a nuclear probe and noble gas analysis, determining that the Hypatia stone (named after the famous Western woman astronomer and mathematician, Hypatia of Alexandria) didn’t come from any recognized comets or meteorites. Recently, the University of Johannesburg researchers returned to the case to answer the looming question: Where did this mysterious rock come from? The answer, published in Geochimica et Cosmochimica Acta in December, may cause us to rethink the materials that formed our solar system.

Hypatia is thought to be a fragment of an extraterrestrial rock originally several meters long, which segmented into numerous pieces during its journey to Earth. It has a mineral composition unlike that of any meteorite we’ve seen. A chondritic meteorite’s chemical composition, for example, is similar to Earth’s, with high amounts of silicon and low amounts of carbon. (Chondritic meteorites are extremely common, making up about 86 percent of known meteorites.) Hypatia’s composition, however, is just the opposite, with unusually high amounts carbon and low amounts of silicon.

"Even more unusual, the matrix (the stone, inside which dust grains are embedded) contains a high amount of very specific carbon compounds, called polyaromatic hydrocarbons, or PAH, a major component of interstellar dust, which existed even before our solar system was formed,” said Prof. Jan Kramers, who led the study, in a press release.“Interstellar dust is also found in comets and meteorites that have not been heated up for a prolonged period in their history.”

Oddly enough, the majority of PAH in the matrix turned into tiny diamonds, no larger than one micrometer, likely due to the immense heat and pressure when Hypatia made contact with Earth’s atmosphere or surface. However, the diamonds weren’t the only surprise that researchers came across when they analyzed the mysterious stone. Geologist Georgy Belyanin also found unexpected chemical elements in the interstellar dust grains embedded throughout the stone, including a rare form of aluminum.

"The aluminum occurs in pure metallic form, on its own, not in a chemical compound with other elements. As a comparison, gold occurs in nuggets, but aluminum never does. This occurrence is extremely rare on Earth and the rest of our solar system, as far as is known in science," said Belyanin. "We also found silver iodine phosphide and moissanite (silicon carbide) grains, again in highly unexpected forms. The grains are the first documented to be found in situ (as is) without having to first dissolve the surrounding rock with acid," adds Belyanin. "There are also grains of a compound consisting of mainly nickel and phosphorus, with very little iron; a mineral composition never observed before on Earth or in meteorites."