Found on the surface of any piece of pure aluminum will be a thin super-thin (it's practically one molecule in thickness of aluminum oxide). It's so thin it's practically not there - but yet in reality it's always present. In normal conditions the chemical reaction between al and oxygen cannot be avoided. Aluminium oxide is responsible for the resistance of metallic aluminium to weathering. Metallic aluminium is very reactive with atmospheric oxygen, and a thin layer of aluminum oxide of only a few nanometers thick forms on any/all surfaces of aluminum. The reaction of aluminum when exposed to oxygen occurs in a matter of a few picoseconds - virtually instantaneously. If you were to scratch a piece of aluminum to expose the "fresh" pure aluminum below the surface the aluminum oxide "coating" would again form instantaneously. So - in reality - you and I will go through our entire lives without actually touching elemental aluminum. Perhaps we could achieve this insignificant goal by dipping our finger in molten aluminum! https://apps.dtic.mil/sti/pdfs/ADA425147.pdf Page 5-19 has a diagram of a spark! When aluminum powder burns - it vaporizes the aluminum and produces AlO and Al02 (aluminum oxide) The equations for the gas phase of Al powder burning is shown on page 5-21. https://en.wikipedia.org/wiki/Aluminium_oxide Copy/Pasted: Molten aluminium oxide near the melting temperature is roughly 2/3 [tetrahedral](https://en.wikipedia.org/wiki/Tetrahedral "Tetrahedral") (i.e. 2/3 of the Al are surrounded by 4 oxygen neighbors), and 1/3 5-coordinated, with very little (<5%) [octahedral](https://en.wikipedia.org/wiki/Octahedral "Octahedral") Al-O present.[[19]](https://en.wikipedia.org/wiki/Aluminium_oxide#cite_note-Skinner2013-19) Around 80% of the oxygen atoms are shared among three or more Al-O polyhedra, and the majority of inter-polyhedral connections are corner-sharing, with the remaining 10–20% being edge-sharing.[[19]](https://en.wikipedia.org/wiki/Aluminium_oxide#cite_note-Skinner2013-19) The breakdown of octahedra upon melting is accompanied by a relatively large volume increase (~33%), the density of the liquid close to its melting point is 2.93 g/cm3.[[20]](https://en.wikipedia.org/wiki/Aluminium_oxide#cite_note-20) The structure of molten alumina is temperature dependent and the fraction of 5- and 6-fold aluminium increases during cooling (and supercooling), at the expense of tetrahedral AlO4 units, approaching the local structural arrangements found in amorphous alumina.[[21]](https://en.wikipedia.org/wiki/Aluminium_oxide#cite_note-21)