Dark blue tourmaline is called indicolite or, occasionally, indigolite. Indicolite is often heat-treated to lighten its color and produce a more attractive stone.
An important source for indicolite is Siberia (Russia), where it occurs in yellow clays formed from weathered granites. Fine, bright blue tourmaline has recently been found in Paraiba, Brazil. Other localities include Madagascar and United States.
A lilac to violet-blue or reddish blue variety (first found in Russia) is known as siberite.