Find me one source indicating that amethyst interacts with ethanol or reacts with it, or how that would even make any sense. Because while you gave a nice description of the rock, and why it has it's color, you did not provide any evidence in favor of it's ability to prevent drunkenness.
I this myth is just that, an untrue myth. Amethyst is pretty, and people had weird superstitions in the past. They wore it as a talisman and put it in their cups, but it didn't stop them from getting drunk. It didn't do anything other than look neat. Siloxanes or not.
Very good question, and this open my mind to do some research, i will answer with some sense.
indeed it is based on a mythology, but Perviously, i have made a thesis about silica xerogel (dry),
in the manufacture of silica gel, we must burn a material contains SiO2 inside,
after it heating at high temperatures, silica ash reacted with NaOH to obtain sol sodium silicate, then this sol soaked with acid to forms a gel, then the gel dried and silica xerogel has been forming, determination of silica coincides with siloxane formation that serve as toxic gas absorber. Indeed there is no reaction between amethyst and ethanol, but siloxane react with alcohol can to form silanol.
At room temperature?
With out this, then science can not justify the myth ;)
It also means:
That you can't conclude this. Because the people of yesteryear were not correct, amethyst did not prevent drunkenness.
yes it is, thanks for feedback, it mean my conclusion was wrong, i have to change it now,