Composition of Tourmalines from Hajiabad and Dehgah area, SE Boroujerd

Tourmaline can be found as an accessory mineral in a variety of rocks including leucogranite, pegmatite, quartz veins, and metamorphiccountry rocks in Hajiabad-Dehgah area in SE of Boroujerd city. Tourmaline in pegmatites is coarse-grained, subhedral to euhedral, anddisplays strong to moderate pleochroic blue rimmed by olive green. In contrast, tourmalines from leucogranite, quartz-veins, and hornfelsschist are very fine- to medium-grained, mainly subhedral to euhedral and in some cases zoned. They are strongly pleochroic withgenerally bluish green to brownish olive colors. The replacement of some feldspar grains by tourmaline forming skeletal texture is alsocommon in leucogranite. The tourmaline in pegmatite is Fe-rich schorl (Fe/Fe + Mg = 0.86–0.95), whereas those in leucogranite, quartzveins and hornfels schist are of schorl-dravite composition (Fe/(Fe +Mg) = 0.31–0.61). Tourmalines in all these rock types are aluminous,alkali-rich, with Na being the dominant alkali element present, and they have small amounts of X-site vacancy. However, the distinctdissimilarity is the Zn contents of pegmatite schorl tourmaline (on average 0.02 apfu), which are noticeably lower than those of tourmalinesof schorl-dravite composition (on average 0.13 apfu). The dominant variability in composition of the studied tourmalines seems to becontrolled mainly by the alkali-deficient AlOMg-1(OH)-1 and proton-deficient □AlNa-1Mg-1 exchange substitutions. Tourmaline grains frompegmatite have the chemical features of tourmalines from Li-poor granitoids and associated pegmatites and aplites, whereas those fromleucogranite, quartz-veins and hornfels schist possess the chemical characteristics of tourmalines from Ca-poor metapelites, metapsammites,and quartz-tourmaline rocks.