Solid Mineral of the Week — Elbaite
Elbaite is a sodium, lithium, aluminium boro-silicate, with the chemical composition Na(Li1.5Al1.5)Al6Si6O18(BO3)3(OH)4. It is a mineral species belonging to the six-member ring cyclosilicate tourmaline group.
Elbaite is the most well-known and valuable form of Tourmaline. Most of the multicoloured Tourmalines and almost all of the Tourmaline gemstones are of the Elbaite variety. Elbaite is perhaps the most multicoloured mineral, coming in virtually every colour of the spectrum. Multicoloured crystals of Elbaite are well known and unsurpassed in beauty.
Elbaite has many interesting optical properties. Many green and blue specimens are strongly pleochroic. When viewed through their vertical axis, such specimens appear darker in colour than when seen through their horizontal axis. Certain Elbaites exhibit a cat’s eye effect when polished into cabochons.
The type locality for Elbaite, where this mineral was first described, is on the island of Elba, Italy, in 1913, in the deposits of San Piero in Campo and nearby Sant’Ilario in Campo. These deposits have produced very old historic Elbaite, especially the classic Moor’s Head Tourmalines with black caps.
Elbaite forms in igneous rocks, metamorphic rocks and veins in association with lepidolite, microcline, and spodumene in granite pegmatites; with andalusite and biotite in schist; and with molybdenite and cassiterite in massive hydrothermal replacement deposits.
Among the most noteworthy sources of Elbaite is the state of Minas Gerais, Brazil, where outstanding forms and colours of this beautiful Tourmaline are found in numerous pegmatite localities. Others include Afghanistan, Nigeria (Jos), Northern Pakistan, Madagascar, Namibia, Southern California, New England, Connecticut etc.