This is no doubt a simple question but I’ve not yet figured out an adequate answer on my own. I keep coming across statements like this one:
This process, known as spallation , is how the majority of lithium , beryllium, and boron was formed in our Universe.
But I’ve not been able to find an explanation for how such a not-so-common element gets concentrated in various geologic deposits on earth. All of my Google searches and A.I. engine searches produced results like this one:
Lithium deposits are brine deposits which are formed when lithium-rich waters evaporate and leave behind a concentrated brine of lithium salts.
. . . but which doesn’t really answer my question.
I eventually found an explanation which appeared to suggest that a carbon-nuclei cosmic ray collides with a hydrogen atom to split and create helium and lithium nuclei. But how do large accumulations of those lithium atoms end up in major deposits like those in Chile? Why don’t we find lots of major lithium deposits suitable for mining scattered about the planet? (I assume that Chile wasn’t necessarily singled out for carbon-nuclei bombardment.)
I assume the different elements don’t move equally well throughout the mantle, and over time due to their differences in chemistry and physics (melting temperature, oxidation states and whatever), some tend to collect and concentrate in large deposits as they move through the mantle, that form and grow larger over time in something analogous to how the mechanical action of waves on the beach can sort pebbles by size over time. Not a geologist, but that’d be my best guess.
Fascinating. And a helpful analogy. I wonder how well these kinds of mantle processes are understood.
I wonder if lithium’s low density caused it to gradually rise from the mantle over time. (I realize that the earth’s mantle is not liquid magma, as probably most people wrongly assume—but we know that differential convection does take place.)
Lithium certainly has its notable qualities. Lithium is the least dense of all elements that are solids at room temperature. And it is the only metal that floats on water (has half water’s density.) It has the highest specific heat capacity among solids, which I wouldn’t have guessed but I don’t have a lot of physics background. Of course, it has the greatest electrochemical potential and the highest energy density for a given weight. Pretty cool.
Of course, lithium salts have important uses in psychology. This probably explains why driving an electric car has therapeutic properties. [Yeah, that is an intentionally absurd statement meant to be a lame attempt at humor.]
From delving around, that would be true. The contribution of any spallation production here on Earth would be minuscule. Extent lithium is almost entirely inherited from prior cosmological processes. There is this pertinent discussion from Ethan Siegel.
Glancing around online, most economically viable lithium deposits are from granite pegmatite, which are igneous and not evaporite deposits. Further reading suggests that they form by crystallization, which occurs fractionally by composition such that certain materials that are able to crystallize at higher temps form first, with lithium-bearing crystals being among the last fraction. This would tend to concentrate it.
As I understand it, another vexing problem is: Why isn’t there more lithium in the universe?
One of my patients expressed concern that as electric cars become more common, there will no longer be lithium available for his medication. I was able to reassure him on that account.
I suppose you could also tell him that virtually all medications are derived to some extent from petroleum—yet, the existence of gasoline-based vehicles has not jeopardized the production of medications.