Lithium Minerals - only 13 common Lithium minerals
Eucryptite (LiAlSiO4) at 5% Lithium is the best I can do for a Lithium APEX Mineral.
Lithium must be stored under oil since it is quite reactive with air and water.
Lithium commonly only appears as a soluble ionic compound. Most lithium is found as dissolved salts in the ocean or as evaporite deposits (which are eagerly mined).
Lithium is used as a flux in welding processes and is also used in electrical applications including batteries.
It is not known whether Lithium has a physiological role in any organisms but nutritional studies in mammals have indicated its importance to health, leading to a suggestion that it be classed as an essential trace element.
Lithium starts row 2 (Period 2) on the periodic table. This is the row which gave me the most trouble. You would think the most common elements here on row 2 would be the easiest. It turns out that each element here has its own interesting story.
Row 3 and higher are generally less exciting stories to tell. Most elements have a variety of minerals to collect and there are many subjective choices to make as far as what is collectible.
OK. Back to Lithium. It turns out that Lithium and it's next 2 neighbors, Beryllium and Boron are a little special. All 3 of these elements are much less abundant in the universe than other early elements. Why is that? The stellar processes which create elements do not normally create these 3. The nucleosynthesis pathways just aren't there. A common thesis says that these 3 elements were all created at the time of the big bang only. Maybe. But the fact is that they are pretty scarce. So here on Earth, the concentrations are low.
Lithium that does exist is also easily destroyed in stars at low temperatures. The nuclei of the 2 common Lithium isotopes verge on instability because they have such low binding energies.