Why Black Tourmaline is So Dense and Heavy?

Black tourmaline, also known as schorl, is a common mineral that is found all over the world. It is popular among collectors and crystal healers for its black color, striated appearance, and reputation for protective properties. But one of the most notable physical properties of black tourmaline is its relatively high density and weight compared to other common minerals. So why exactly is this dark crystal so heavy?

The high density of black tourmaline can be attributed to a few key factors relating to its chemical composition and crystal structure. The chemical formula of black tourmaline is complex, but it essentially contains a high concentration of iron along with other dense elements like sodium, aluminum, silicon, and boron. The abundance of iron is partly why the crystals are so dark in color. These heavier elements pack tightly together in the tourmaline crystal structure.

The crystalline structure itself also plays a role. Tourmaline crystals have a trigonal crystal system and grow in long vertical striated prisms. This ordered alignment of molecules and atoms allows more mass to fit into a given space. The long column-like shape maximizes density.

In addition, tourmaline rates between 7 and 7.5 on the Mohs hardness scale, so the molecular bonds holding the crystals together are relatively strong. This further contributes to the compact nature of the mineral. The combination of these properties produces a crystal that feels noticeably heavier than many other common minerals.

While the exact density can vary based on a particular sample’s composition, black tourmaline has an average density around 3.06 g/cm3. This is significantly denser than examples like quartz at 2.65 g/cm3, calcite at 2.71 g/cm3, and fluorite at 3.01 g/cm3. So a piece of black tourmaline of the same volume as those lighter minerals will weigh much more.

The high density and weight of black tourmaline can also make it easier to identify among mineral collections. A good way to test if a dark striated crystal is tourmaline is to simply heft it in the hand. If it feels exceptionally heavy for its size, it most likely is black tourmaline. So next time you come across an unknown yet heavy crystal, the density itself provides a clue that it may be this dark variety of tourmaline.