Serendipity. Last night I just finished carving a 30ct Morganite. The
stone had been preformed and had gone through a workshop fire,which
had caused it to be heated to at least 450 C ( my estimate) The
result was a non facetable stone that had the typical 'rainbow'
feathers one sees in heat treated Aquamarine rough. Anyway, I was
carving, using diamond burrs and "chasing" the fractures. Bad move.
They don't stop. They just continue as if once the crystal has been
split, it runs like a windscreen crack. The only way I got them to
stop is to go to a finer grit and then into polish. This might be
something that happened to your Aqua. Or is happening.As you pressed
on the stone that crack said "Hi, I am visible now, just follow me"
Most certainly, in my opinion, it is a weak, but not really terminal
point of that stone. I am not saying your Aqua is treated, but my
morganite certainly was. Also, before the fire, the Morganite was
that typically dusty pink/brown they are sometimes. After carving
it, it is a lovely pure pale pink. So good came after trouble (grin)