A member of the cyclosilicates and a borosilicate Na(Mg,Fe2+,Mn,Li, Al)3Al6 (BO3)3[Si6O18](OH,F)4. There are three important members of this family of minerals: dravite (NaMg3Al6(BO3)3[Si6O18] (OH,F)4); schorl (Na(Fe2+,Mn)3Al6(BO3)3[Si6O18](OH,F)4); and elbaite (Na(LiAl)3Al6(BO3)3[Si6O18](OH,F)4); sp. gr. 2.9–3.2; hardness 7.0–7.5; trigonal; black, bluish, pink, or green, never colourless; elongate crystals common, also acicular needles and massive or radiating aggregates; cleavage good {1120} prismatic; occurs in granite pegmatites, pneumatolytic (see pneumatolysis) veins, and granites as elbaite and schorl varieties; it may occur in the rock luxullianite formed by pneumatolytic action after boron has been introduced, where it will occur with topaz, spodumene, cassiterite, fluorite, and apatite. Dravite variety occurs in metamorphosed impure limestones and rarely in some basic igneous rocks; tourmaline is a common detrital ‘heavy’ mineral in sedimentary rocks. Good multicoloured crystals can be used as gemstones.