Next time you wash your laundry with borax, pause for a moment and consider the path those boron atoms took to get to your dirty shirts.  The Big Bang started the universe with H, He, and maybe a bit of Li.  The rest of the periodic table had to be produced by nuclear reactions within the core of a star or during the explosion of a star.  This occurs through either the fusion of charged nuclear particles (nuclei included) or absorbed neutrons to nuclei, perhaps followed by a decay cascade.  Note to reader: astronomers are in the habit of referring to elements heavier than helium as a “metal”. 

In the core of a star there exists a complex kinetic circus of multiple simultaneus synthetic channels involving both atomic weight buildup and disintegration.  Nuclei less sensitive to the reaction conditions may accumulate and delicate nuclei like boron have but a fleeting existance and are consumed.  In addition to stability to the reaction conditions, particular combinations of protons and neutrons tend to be more stable and accumulate if only by the lack of propensity to decay. 

While the elements C, N, and O are cosmically quite abundant, at least in comparison to the rest of the elements (3 to 92), the elements Li, Be, and B (LiBeB) are relatively scarce. 

Because boron was too heavy for Big Bang nucleosynthesis and too reactive to accumulate in a stellar core, it’s cosmic abundance is low.  What little that is found did not arise as simple boron ejecta mechanically boosted into the interstellar medium by an explosion or as entrained mass from stellar wind.  It was formed from more abundant elements like CNO that had already been ejected- elements that would be subjected to a barrage of highly energetic particles.

LiBeB are thought to be “spallation” products from interstellar CNO collisions with cosmic rays.  From the linked chart, we can see that C, N, and O are relatively abundant.  So over a multibillion year timeframe of stellar evolution, early massive stars can live and die, dispersing metals into nearby space.  Accumulated heavy elements can then be exposed to cosmic ray fragmentation.  The source of the cosmic ray particles in these collisions is somewhat up in the air.  Some of the latest thinking suggests that these energetic cosmic rays yielding spallation products are from especially energetic sources like Wolf-Rayet stars or type II supernova events.  There is an indication that boron can come from two spallation channels- cosmic ray and neutrino-induced spallation of carbon. 

So, the picture thus far- boron arises from the energetic collision of particles outside of a star.  Heavier nuclei will fragment under cosmic ray bombardment and some combination of B-11 and B-10 are formed.  What is interesting is that this is a dispersive phenomenon.  By contrast, on earth, boron is found in deposits as the hydrate of the alkali metal salt of the oxide- Borax.  There are a variety of distinct mineral compositions that contain boron.  On earth, a bit of the dispersed boron was somehow concentrated into ore bodies.  This is where geology kicks in.

Hydrothermal action near subduction zones can dissolve borates in hot, pressurized water and deposit them at the surface where the solid borates come out of solution on cooling.  This process evidently partitions the isotopes of Boron slightly.  Over time the process continues until geological events interrupt the deposition process.  If the solubility of the borates is relatively low at surface temperatures and pressures, then weathering will not further disperse them into the hydrological cycle.  Thus they form a deposit.  Layers of sediment accumulate over the borax deposit and eventually geological processes move the layer underground. Eventually, uplifting, weathering, and mining makes the deposit accessible.  Through the miracle of marketing, distribution, and 18-wheeler trucks, this spallation product can be used to clean that unsightly mustard stain from your shirt.

News Flash! Most energetic supernova ever observed was detected in the galaxy NGC-1260 by Chandra.