10" Black Tourmaline (Schorl) Covered In Mica - Brazil

Schorl, also known as "black tourmaline" or "black schorl", is a black form of tourmaline that often occurs as lustrous prismatic crystals. The crystals can be stubby or elongated and typically feature lengthwise striations. Many schorl crystals have flattened pyramidal terminations. They can also form in radiating, columnar, and stalactitic aggregations, as well as small, needle-like inclusions within quartz (tourmalinated quartz) and in massive form.

Schorl is a basic sodium iron aluminum boro-silicate with the generic chemical formula NaFe2 + 3Al6(BO3)3Si6O18(OH)4 . It has been used for everything from jewelry to piezoelectric guitar pickups.