A minor source of lithium is spodumene and petalite. Commercial quantities of spodumene and petalite occur only in a very coarse-grained, granitic intrusive igneous rock known as "pegmatite". Although lithium is found in lepidolite, the known occurrences of lepidolite are typically far too small and dispersed to be an economical, useful source of lithium.
The major source of lithium are brine and lake sediments that contain lithium carbonate. The largest reserves of lithium rich brine is the playa lake sediments of Salar de Uyuni, Bolivia. The high concentration of lithium in the brines and sediments of playa lakes were created by the concentration by evaporation within these lakes of lithium leached by weathering from volcanic rocks in surrounding mountains.
Lithium is also obtained by the mining and processing of hectorite. Hectorite was created by the alteration of volcanic ash that accumulated within saline lakes. The major source of hectorite is the Hector Mine, Hector, San Bernardino Co., California.
Lithium - http://www.mii.org/Minerals/photolith.html
Pegmatite - http://en.wikipedia.org/wiki/Pegmatite
Salar de Uyuni - http://en.wikipedia.org/wiki/Salar_de_Uyuni
In search of Lithium: The battle for the 3rd element
Hectorite - http://www.mindat.org/min-1841.html