Buzzword Bingo: What are Critical Minerals, Rare Earths, and Minor Metals?

Is cobalt a rare earth element? Is uranium a critical mineral? And what’s the difference between minor metals and rare earth elements? I doubt anyone woke up this morning wishing they knew the answers to these questions, but future posts will throw these terms around – and mainstream media often mixes them up – so it’s probably worth us all getting on the same page first.

What are Critical Minerals?

The term “critical minerals” is essentially an invention of the U.S. government. While the two words have appeared in the same sentence for decades, the term itself wasn’t commonplace until recently. Even now, most Google searches for “critical minerals” appear in the United States – specifically, Washington, D.C.

The Energy Act of 2020 defines a critical mineral as a non-fuel mineral or mineral material essential to the economic or national security of the U.S. and which has a supply chain vulnerable to disruption. The U.S. Geological Survey’s (USGS) list of critical minerals is generally considered the definitive one; the 2022 list contains 50 minerals. The USGS released an accompanying Methodology and Technical Input document which ranks each mineral based on assessed economic vulnerability and disruption potential. The document has some nifty graphics, one of which is included below.

Side note: the 2022 list drops uranium since it’s classified as a “fuel mineral.” Per the Energy Act of 2020’s definition, it can’t be a “critical mineral” despite its importance to economic or national security. That’s provoked a good deal of annoyance in congressional hearings.

However, the Department of Energy (DOE) has issued an energy-specific critical materials list which differs in two significant ways: it’s forward-looking (whereas the USGS list assesses current criticality) and it takes an energy-specific view. The Department’s Critical Materials Assessment is a solid read for those interested in reading a 111-page report… though the two graphics on p. xiv are essentially the bottom line. The second one is below.

The Defense Logistics Agency’s Strategic Materials division also maintains its own list of defense-specific minerals, though it isn’t cited as frequently as the USGS or DOE lists.

So, a critical mineral is any mineral that is important to economic or national security but is also vulnerable to disruption. Iron meets the first criterion but not the second since we produce a good deal of it in the United States. Same goes for molybdenum and beryllium.

While USGS and DOE have both introduced quantitative measures to help explain their decisions, and to deflect some of the political pressure they’ve recently experienced, some subjectivity is inherent to the process for at least three reasons.

First, timeframe matters. The minerals that are important to today’s economy – but also vulnerable to disruption – won’t necessarily be on the list 5-10 years from now. Given that mines in the U.S. take more than a decade to progress from exploration to full-scale production, one can argue that today’s lists ought to take future trends into account – but without a crystal ball, any prediction of future trends is going to be subjective.

Second, reasonable people can disagree about what’s most important to the U.S. economy. Perhaps we should prioritize minerals associated with defense technology over those associated with solar panel production, or nuclear power over EV battery production. Are semiconductors are more important than any of those since dominance in AI could determine future economic and military power?

Third, geopolitics matters when we consider vulnerability to supply disruption. A future post will discuss geopolitics and history in more detail, but there is plenty of debate over whether any given country – much less trends in foreign direct investment – should be considered a current or future threat to national security.

Minerals vs. Metals vs. Materials

Minerals vs. metals first. You can look at minerals and metals as a Venn diagram with a good deal of overlap.

Minerals have a few major characteristics:

• Substances that occur in nature

• Solid and won’t drip, evaporate, or melt

• Are inorganic (not carbon compounds)

• Have a crystalline structure (a distinct arrangement of atoms)

Metals are any element with a positive electrical charge. They’re typically good conductors of heat or electricity, and all are malleable (can be formed into thin sheets) or ductile (can be drawn into wires).

Geologists will hate the simplification that follows, so my apologies in advance – but many metals don’t occur in nature and therefore aren't considered minerals. Similarly, many minerals aren't metals, but some contain metallic elements. Bauxite being refined to create aluminum is one example.

Materials are a catch-all to describe minerals, metals, and... well, materials that don't fall into either category.

What are Minor Metals?

“Minor metal” is a widely recognized industry term for a category of metals whose production is very small relative to base metals like iron and copper – and they’re usually produced as by-products while producing base metals. For instance, bauxite is refined into alumina (and then aluminum) but gallium can be extracted in the process. Cobalt is a by-product of either copper or nickel production. Many minor metals were historically discarded since it wasn’t economical to extract them, but that’s starting to change since many of those metals have become central to high-tech products – and have thus found their way onto critical minerals lists.

The fact that minor metals are usually tied to the production of base metals is part of the reason why their prices are so volatile. Their supply is often completely separated from demand because they are usually just a tiny fraction of a given mining company’s or refiner’s revenue. Let’s say gallium is badly needed and its price has spiked 200% in the past year. It constitutes such a small portion of bauxite that the price of bauxite will barely budge. Is a bauxite miner really going to double or triple its production to help an alumina producer meet gallium demand? No.

Perhaps a few more alumina production plants will activate or build gallium production capabilities, but that’s easier said than done. Factor in the opaque market – gallium isn’t traded on any exchange – and you get wild price fluctuations that would never occur with a base metal.

What are Rare Earths?

Rare earths, or more properly, rare earth elements (REEs), are the lanthanide series on the periodic table, plus scandium and yttrium since those elements exhibit similar properties. REEs fall into two buckets based on atomic weight: light (LREEs) and heavy (HREEs). Scandium and yttrium are also considered HREEs.

At least one future blog post will include a detailed discussion about REEs. For now it’s worth noting that they all fall within the critical mineral bucket, but some – particularly neodymium, praseodymium, and dysprosium – are far more “critical” than others.

Calling REEs “rare” is a bit of misnomer since many are abundant in the earth’s crust; they just rarely occur in concentrated enough deposits to be recoverable and separating them is a difficult process, to put it mildly. Many of the recoverable REEs are in China due to a combination of geologic good fortune and decades of targeted industrial policy.

For those who made it through this slog… kudos. I hope this is the driest post I’ll ever write. The graphic below is the same one at the top of the post, though now perhaps it’ll make a bit more sense and will trigger another set of high school chemistry flashbacks.

Credit: National Energy Technology Laboratory, U.S. Department of Energy (2022)