I think we can safely assume that when you say that it melted, you
were referring to the metal! However, for those people who asked
about what ultimately happens to aquamarine when you heat it, read
Aquamarine shouldn’t really be soldered in-place. It can fade or
change colour at temperatures as low as about 600 degrees centigrade.
It isn’t possible to ‘melt’ aquamarine, but this is just because it
decomposes into a different mineral. You will need a temperature of
well over a thousand degrees: firstly the beryl begins to decompose
and it turns opaque (looking like porcelain), then ultimately it
bubbles and turns into a type of liquid glass. However, once it
decomposes, there’s no way to turn it back into aquamarine - so,
unfortunately, you can’t cast it!
If it was the stone itself that melted, then it must have been a
fake, like plastic, glass or possibly a synthetic.