File:Aluminium alt 1.svg

Summary
Found in a diagram at alchemy symbols with meanings - the cited source is A compleat body of chymistry by Nicaise Le Febvre (1670), but Aluminium wasn't discovered until the 1800s due to the difficulty of refining it. It looks like it might be a variation of the symbol for antimony, which is another metalloid with a similar lustrous grey appearance.

According to the Dictionary of Occult, Hermetic and Alchemical Sigils, this is also an alternate symbol for antimony, sourced from