The crystal-chemistry of 13 elbaite-schorl tourmaline crystals from the Cruzeiro pegmatite (Minas Gerais, Brazil) was studied with a multi-analytical approach (SREF, EMPA, SIMS, MS). Effective cation radii at the Y and Z sites and site populations were reÞ ned by a minimization procedure. The results indicate that the crystals belong to the alkali group. Elbaite crystals are O 2– -free at the W and V sites and show OH content at the O2 site (up to 0.2 apfu). Conversely, schorl crystals always show O 2– at the W site. The main substitutional mechanism is the dehydroxylation type: Y Fe 2+ + Y Fe 3+ + W O → Y Li + Y Al + W (OH+F).