achroite

(from the article `tourmaline`) ...usually recognized: iron tourmaline (schorl), black in colour; magnesium tourmaline (dravite), brown; and alkali tourmaline, which may be pink ...
Found on http://www.britannica.com/eb/a-z/a/12

Achroite

A white potassium-rich variety of tourmaline.
Found on https://www.encyclo.co.uk/local/20501
No exact match found