Properties of Tourmaline

Tourmaline is a crystalline boron silicate mineral with complex and variable chemical compositions. It is well-known for its wide range of colors, which can include black, brown, green, pink, red, blue, and multicolored varieties.

Image of tourmaline mineral
Credit: Rob Lavinsky, iRocks.com - CC-BY-SA-3.0, via Wikimedia Commons

The following table provides a comprehensive list of tourmaline properties in both SI and US customary/Imperial units at normal temperature and pressure (NTP).

Note: click on the icon to switch between Metric and Imperial units.

Table of Tourmaline Properties
Physical Properties
Metric
Chemical FormulaNa(Mg,Fe,Mn,Li,Al)3Al6Si6O18(BO3)3
Crystal SystemTrigonal
Mohs Hardness7 - 7.5
Density3140 kg/m3
DiaphaneityTranslucent to opaque
LusterVitreous, resinous
CleavageIndistinct
FractureUneven
StreakWhite

Note: unless stated otherwise, all values are taken at room temperature (approximately 20°C or 68°F) and 1 atm pressure. (1 atm = 101,325 Pa)

Related Pages
References: 1) Cardarelli, François. Materials Handbook: A Concise Desktop Reference. Switzerland: Springer International Publishing, 2018. 2) CRC Handbook of Chemistry and Physics, 97th Edition. United Kingdom: CRC Press, 2016-2017.