Black Tourmaline

The photo shows three black, raw, unpolished pieces. Their faces have deep grooves running along the crystal, like corduroy made of stone. This is black tourmaline, known to mineralogists as schorl. According to Wikipedia, schorl is the most common kind of tourmaline, and it may account for 95% or more of all tourmaline in nature. For its colorful siblings, see the multi-colour tourmaline page.

The grooves are its trademark. According to Minerals.net, schorl crystals are usually long and deeply striated along their length, and many of them have a rounded triangular cross-section. And according to Minerals.net, schorl is always black, and unlike other tourmalines, it is never transparent, not even slightly. So if you can see through it, it is not schorl.

The name has a story too. According to Wikipedia, the name "schorl" was in use before the year 1400, because a village in Saxony, Germany, was then called "Schorl". Near the village was a tin mine, where black tourmaline was found along with the tin. Today the village is called Zschorlau. It gave its name to the stone, and then changed its own.

It has an electric side as well. According to Minerals.net, schorl is strongly pyroelectric, meaning it becomes charged when heated, and it is also piezoelectric, becoming charged when squeezed. According to Crystal Vaults, Dutch traders in the 18th century knew about this, and used tourmaline to pull ash out of their pipes. They called it Aschentrekker, the "ash puller". An 18th-century vacuum cleaner.

According to Geology.com, black tourmaline occurs as a minor mineral in many rocks, such as granite, pegmatite and gneiss, usually in small amounts. And according to Minerals.net, especially fine crystals come from Pakistan, Namibia, Madagascar and Brazil. Collectors love it, and it is sometimes cut as a black gemstone too, although according to Minerals.net that is not common.