Tourmaline (or tourmaline) is a semi-precious crystal with a variable chemical structure and a complex silicate of aluminium and boron. Atoms of sodium, calcium, magnesium, iron, lithium, etc. can be substituted for aluminium atoms in varying proportions, resulting in variations in the physical properties of the crystal. Tourmaline is one of the minerals with a trigonal crystallisation system. The chemical formula shows that hydroxyl ions (-OH) and fluorine ions (-F) can combine in different mixing ratios with metals; this mixture determines the colour and hardness of the mineral (between 7 and 7.5).
Tourmaline colours are very varied, ranging from blue, green, red, pink, brown and black. Sometimes one crystal can have more than one colour; in cross-section, some crystals appear as an agate with concentric circular lines of different colors. Tourmalines often show the phenomenon of pleochroism, i.e., changing colour depending on the direction of observation. The most common pleochroism is from blue to black.
Another property of tourmaline crystals is piezoelectricity, which manifests itself in the electrical polarisation of the crystal as a result of a mechanical action (pressure or torsion) applied to a certain axis of the crystal. Most tourmaline varieties also exhibit pyroelectricity, i.e., the occurrence of electrical polarisation when the crystal is heated or cooled. Tourmaline is the first material in which these two properties have been observed.
The term tourmaline came into Romanian from other European languages (German Turmalin, French tourmaline). However, the origin is the Sinhalese (the majority language spoken in Sri Lanka) word turamali, meaning'stone that attracts ash', which reflects tourmaline's pyroelectric properties.
English
Română
