Glass breaking by itself...
Glass breaking is an ill omen. Whatever it may be cannot continue forever. Have caution.
Glass breaks due to it just becoming fragile over time or not made right in the first place and any vibration can cause it to break just like high pitch sounds......... It's not an ill omen, sheesh ppl.
I doubt very seriously it was the amethyst Crystal. There are many recorded cases Spirit breaking glass. A burning candle in the glass could easily do it. But a crystal having sufficient energy to crack the glass is highly unlikely considering the crystal is made of silica as well. If the glass is breaking for no apparent reason then the culprit may in fact be spirit.
When glass usually breaks its a spirit trying to get your attention..
Spontaneous break of glas isn't even that rare. It is a physical matter of residual stress.
It is interesting