Liddicoatite - Encyclopedia
Class : Silicates
Subclass : Cyclosilicates
Crystal system : Trigonal
Chemistry : Ca(Li,Al)3Al6(BO3)3Si6O18(O,OH,F)4
Rarity : Very rare
Liddicoatite is a very rare variety of tourmaline close to elbaite : the sodium of the latter being replaced by calcium. It is a tourmaline from sodolithic pegmatites, especially encountered in eluvium resulting from their dismantling. It was named in honor of the American gemologist Richard Thomas Liddicoat of the GIA. Like the majority of minerals in the tourmaline group, it is almost always well crystallized, in stocky prisms strongly striated according to elongation, with a triangular section with curved edges, and pyramidal endings. Its colors are very variable, it is famous for its triangular growth streaks variously colored in green, pink, yellow or brown. It is impossible to distinguish it from elbaite without laboratory analysis. Liddicoatite has a very limited use in jewelry and ornamentation given its rarity ; it is commonly cut into polished slices to highlight its zoning.
Main photo : 9.3 cm liddicoatite crystal from Sahatany Valley, Ibity, Madagascar
Liddicoatite in the World
Twinning
No twin known for this mineral species.
Fakes and treatments
No fakes recorded for this mineral species but very hard to differentiate from other tourmaline species.
Hardness : 7.5
Density : 3.02
Fracture : Irregular to conchoidal
Streak : White to light brown
TP : Translucent to transparent
RI : 1.630 to 1.651
Birefringence : 0.018 to 0.021
Optical character : Uniaxial -
Pleochroism : Visible
Fluorescence : None
Solubility : Insoluble
Magnetism : NoneRadioactivity : None