What is hydro tourmaline?

A group I belong to orders gems from a supplier who we know
personally. She sent us a new cut to try, and said it was hydro
tourmaline. I’ve tried to find a definition of hydro tourmaline and
was hoping one of you could explain it to us. Thank you!

Laura S-A
Rosaries and Jewelry by Laura

It is hydrothermally stabilised tourmaline. This is a technique
where you basically recrystallise a mineral to get rid of its
imperfections and/or improve it colour. Quartzes topazes and emeralds
are the commonest but it can be done to many minerals. You can also
grow bigger crystals from a seed crystal in the same way. All done in
a pressurised vessel with water and heat. It mimics the conditions
found in volcanic economic deposits.

Nick Royall