New stuff from really old rocks.

A recent article in caught my (and several other people’s) eye. Chi Ma, et al., “Panguite, (Ti⁴⁺,Sc,Al,Mg,Zr,Ca)_1.8 O₃, a new ultra-refractory titania mineral from the Allende meteorite: Synchrotron micro-diffraction and EBSD,” American Mineralogist , July 2012, v. 97, no. 7, p. 1219-1225.  Now I’m not a geologist.  Most of the “meteorites” that I study are still in space, and I don’t know the author at all.  Why am I excited about it?  Therin lies the story…

On February 8, 1969 thousands of rocks fell from the sky over an area some 300 km² is size near the village of Pueblito de Allende in Chihuahua Mexico.  Now known as the Allende meteorite, it stands as one of the most famous and important meteorites in modern times.  Why is that?  Well Allende’s main claim to fame is that it extremely primitive, or in other words, it is really honking old, and is basically unchanged from the earliest times of the Solar System.  It is known as a carbonaceous chondrite, a class of meteorite that are very dark and rich in volatiles like water and (sometimes) organics.  Some carbonaceous chondrites have been known to sweat water when heated.

The fact that these meteorites exhibit that trait indicates something striking – they were never part of a very large parent body (asteroid).  If that was the case the heat generated by the formation of slamming all these small rocks together, and the mutual heat generated by the natural decay of radioactive nucleotides would have radically changed the composition of these rocks.

Allende in particular is know to have in it many, tiny, little white bits trapped within the generally dark matrix that makes up the bulk of Allende meteorites.  These little white bits are called calcium-aluminium inclusions, or CAIs. 

Above is a slice of Allende with a couple prominent CAIs visible.  It is these CAIs that hold the Solar System’s clock.  They were the (some of) the very first high temperature solids to form in the Solar System.  When someone says that the Solar System is 4.57 billion years old, they are really saying that these first solids (the CAIs) formed that long ago (age “zero” for a rock is when it crystalizes/becomes solid).  Essentially, meteorites like Allende are the left over building blocks of the Solar System.  Put enough together you get Mercury.  Put enough together you get Mars.  Put enough together and you get the Earth.  They are the most primitive bits of Solar System solids, older than any rock we can find on large bodies like the Earth, Mars, or even the Moon.  These CAIs have basically the same elemental composition as the early Sun (excluding gasses of course), and CAI bearing meteorites like Allende preserve these pre-Solar System grains - samples of what the Solar System itself was like almost 4.6 billion years ago!

Now, back to the Chi Ma, et al., 2012 paper.  Take apart the title and you have the story: they found a brand new high temperature mineral, now officially named “Panguite,” in samples of Allende.  The same Allende that fell in Mexico in 1969, was collected and has been studied for over 40 years!  Allende, one of the most famous and well studied meteorites in history still has many secrets to reveal – and that’s one of the things that makes planetary science, astronomy, and science in general, great to me:  It always has some new way of surprising you, whether it is bizarre, unexpected features on the first images of a new world or brand new minerals being found in rocks that have been continually studied for half a century.

Science just plain rocks.  Sorry, had to make the obligatory geology joke there.

Panguite is ready for its close up as seen in Figure 2 from Chi Ma, et al., 2012.