Tourmaline with minor amounts of
Zinwaldite (mica).
Tourmaline in Quartz
A Tourmaline
crystal spray in Muscovite mica
Schorl
Schorl
in a granitic pegmatite. Locality - Bradshaw Mountains of central
Arizona
These three connected pictures show the "top", side and "bottom" view of a
tourmaline (schorl) crystal.
Two views of a crystal of Schorl.
Two views of a crystal of Dravite.
TOURMALINE IS A GROUP NAME the group is divided as follows
|
THE TOURMALINE GROUP |
||
|
Mineral Name |
Colors |
Composition |
| Schorl | Black | NaFe3B3Al3(Al3Si6O27)(OH)4 |
| Dravite | Green, brownish, reddish | NaMg3B3Al3(Al3Si6O27)(OH)4 |
| Uvite | Black to white | CaMg3Al3(Al3Si6O27)(O,OH)4 |
| Elbaite | Any color | Na(Al,Fe,Li,Mg)3B3Al3(Al3Si6O27)(O,OH,F)4 |
CRYSTALLOGRAPHY Hexagonal
CRYSTAL GROWTH AND HABITS Tourmalines commonly form long prismatic crystals up to several feet in length. The crystals also often form in loosely radiating clusters. Single crystals may have a flat (pinacoidal) termination on one and a rhombohedral (3 sided) termination on the other, thus demonstrating hemimorphism.
COLOR AND OTHER OPTICAL PROPERTIES Any color, opaque to transparent
HARDNESS 7 - 7.5
SPECIFIC GRAVITY 3.0 - 3.3
LUSTER Vitreous
STREAK White
BREAKABILITY Species of the tourmaline group have poor prismatic cleavage and uneven to conchoidal fracture.
OCCURRENCE Found in coarse grained igneous rocks and pegmatites. Tourmalines are also found in mica schists.
ASSOCIATED MINERALS Quartz and feldspars
NAME from "turamali", a name given to early gems from Ceylon
Schorl - Perhaps from the old German "schurl" meaning impurity
Uvite - Named for its occurrence in the Uva Province in Sri Lanka
Elbaite - From its occurrence on the island of Elba, Italy
Dravite - Named after the Drava River in Austria and Slovenia