Typically sourced from granitic pegmatites in Brazil
(Minas Gerais), Pakistan (Skardu), and Elba Island (Italy), this is a
dark green variety of tourmaline colored by traces of Fe2+ and Mg
within the crystal lattice. The striated prismatic crystals, with their
characteristic pseudo-triangular cross-section, grow here on a matrix
of white calcite (CaCO3), the result of late-stage crystallization in
pegmatite cavities or hydrothermal veins associated with marbles and
metamorphosed carbonate rocks. Hardness 7–7.5 Mohs, density 3.0–
3.2 g/cm³, no cleavage, strong pleochroism.

A specimen highly sought by collectors
for the color contrast between the dark green tourmaline and the
white calcite; also used in jewelry when crystals are of gem quality; a
piece of great educational value for illustrating pegmatite
paragenesis.