Take the road north from Plympton in Devon, just outside Plymouth, and after a couple of miles driving past fields and solar panels, you will see what looks like a big, artificial hill rearing up to your right.

This mound may not look like much, but it is a glimpse of one of the most important industrial sites in Britain.

Not that you'd guess that from afar, or, for that matter, from inside. When I visited the Hemerdon site a few months ago, it was almost completely deserted. But here, beneath the ground on the edge of Dartmoor, is one of the world's biggest troves of tungsten.

Tungsten is a substance of superlatives. Phenomenally hard, extraordinarily strong and incredibly dense, it has the highest melting point of any metal. And, thanks to these properties, it is an essential ingredient in how we make the modern world.

Advanced semiconductors – computer chips – rely on tungsten for some of their critical junctions and connections.

Tools and drills use tungsten for its hardness. And, perhaps most relevant of all these days, it is a crucial component in weapons and armour. If you are going to war, you need tungsten.

All of which is why there is a race underway to procure as much as possible of this metal. Tungsten is what governments around the world call a 'critical mineral'. It is one of a suite of such substances without which civilisation as we know it would crumple.

Without critical minerals we cannot build the technology that powers the World Wide Web; we couldn't make the machines that keep us alive or the ones that defend us from our enemies. But since many of these metals are scarce and since demand for them is on the rise, countries around the world are competing to get their hands on them.

Tungsten West Mine in Hemerdon, Devon. This mound may not look like much, but it is a glimpse of one of the most important industrial sites in Britain, writes Ed Conway

A quartz mine in North Carolina which could supply growing demand for AI chips as every silicon chip in the world depends on the minerals being dug out of a single vein of rock at this site

China restricted exports of seven heavy and medium rare earth elements and the components made with them, gumming up the supply chains manufacturing motor cars and electronics around the world

Cold War-era hangars are now storing stockpiles of obscure metals. Geologists are travelling to far-flung lands, drilling thousands of feet below the ground and pushing the limits of technology to acquire them. And, all of a sudden, critical minerals are playing a key role in the brewing trade war.

Tungsten is just the start of it. When Chinese and American officials gathered in London for talks a few weeks ago, the negotiations hinged on a very particular category of minerals: rare earths.

Rare earth metals are a set of elements that occupy their own section at the very bottom of the periodic table. These metals play an important role in defence and technology. From fighter jets to wind turbines to the earphones you might use, rare earth metals are everywhere in our lives.

Yttrium makes steel alloys far tougher and more resilient. Neodymium makes far more powerful magnets. But the vast majority of rare earths are mined and refined in China.

Beijing already has a near stranglehold over these materials and the products made of them. So when, in April, it deployed them as an economic weapon, it sent shudders through the global economy.

China restricted exports of seven heavy and medium rare earth elements and the components made with them, gumming up the supply chains manufacturing motor cars and electronics around the world.

Rare earths proved more than a match even for the great negotiator himself: they, more than anything else, forced Donald Trump to compromise on tariffs with the Chinese.

Though even now it's still unclear whether China will lift its restrictions any time soon.

Ed Conway is economics editor of Sky News and author of Material World

Most of the world's cobalt is to be found in the Democratic Republic of the Congo. Picured: A mining site in Kolwezi, Democratic Republic of the Congo

Tungsten is phenomenally hard, extraordinarily strong and incredibly dense, it has the highest melting point of any metal

Consider a metal such as cobalt. You may not think much in your life depends on this exotic material, but without it your smartphone and laptop wouldn't function, since their batteries depend on a cocktail of lithium and cobalt atoms.

Most of the world's cobalt is to be found in the Democratic Republic of the Congo (DRC), where conditions in mines can be gruesome. Indeed, investing in the DRC is so fraught with risk that many Western companies have abandoned the country, leaving much of the mining to Chinese businesses.

What about the jet engines that power our planes? To make the superalloys you need in their turbine blades you don't just need cobalt. You also need nickel, molybdenum, magnesium and a host of other obscure elements: titanium, rhenium, niobium and chromium.

And what do nearly all of these elements have in common? The fact that China has a near stranglehold on either their production or refining.

The one exception, in this case, is niobium. But since nearly the entire world's supply comes from a single mine in Brazil, this is not especially reassuring either.

Lithium is even more irreplaceable when it comes to modern batteries than cobalt, yet its supply is only somewhat less concentrated. Much of it is to be found in salt flats high up in the Andes in Chile and Argentina. Even more comes from the Australian Outback. Yet what both of these regions have in common is that they ship most of their raw ores and concentrates over to China for processing.

For a long time, most Western politicians chose to ignore this topic, but today that is all changing. They have realised that economic and military supremacy depends not just on barrels of oil but on the minerals that go into batteries and drones, not to mention high-tech weaponry. And so, in what feels almost like a new Great Game, they are scrambling to try to secure them.

Most famous is President Trump's minerals deal with Ukraine, which provides the US with access to the rare earths and lithium in the Ukrainian steppe. And part of the President's fixation with buying Greenland is said to be the mineral riches beneath the territory.

According to the Financial Times, China's acquisition of foreign mines is at the highest level for a decade, with ten deals worth more than $100 million (£73 million) in the past year.

Every week brings fresh stories of new discoveries: rare earths in Kazakhstan; rich veins of phosphates in Norway.

The problem, however, is that with such discoveries, the brutish reality of what it takes to get this stuff out of the ground means they rarely live up to their initial hype. The difficulty of sourcing terrestrial minerals has given rise to a parallel race, into the oceans.

For decades, deep-sea mining was considered a technological and economic impossibility. But now, in an age of AI and advanced robotics, investors believe it is only a matter of time before minerals are extracted from the seabed.

That would mean meddling with one of the last remaining pristine ecosystems on the planet, raising the question: does the demand for critical minerals trump the environment?

No prizes for guessing the US President's answer. He recently gave the go-ahead for deep sea mining in American waters. But here again, he runs into a challenge: China has been investing in the sector for so long that it is widely seen as the world leader.

At this stage you're perhaps wondering, is China dominant absolutely everywhere?

Well, not quite. Consider the parts and materials you need to make the computer chip. Nearly all of the world's advanced semiconductors are made in Taiwan by a company called TSMC. They're the ones making the silicon brains inside pretty much every smartphone.

Every silicon chip in the world –and for that matter every solar panel – depends on the minerals being dug out of a single vein of rock in an obscure part of North Carolina. For the silicon out of which those chips and panels are made can be refined only with the help of what is known as ultra-high purity quartz. And the world's premier resource for this material is Spruce Pine, in the Blue Ridge mountains.

That you probably haven't heard of it is not without reason. Like most of these places, it is happy to operate beneath the radar.

Sibelco, the company that mines most of the ultra-high purity quartz at Spruce Pine, hasn't admitted journalists to its site in decades, if ever. When technicians are brought in to repair machines, they are reportedly blindfolded to prevent them glimpsing the company's methods.

But is it any wonder secrecy abounds, given this business holds the fate of the world in its hands? One former worker told me: 'If you flew over the two mines in Spruce Pine with a crop-duster loaded with a very particular powder, you could end the world's production of semiconductors and solar panels within six months.'

Last autumn Hurricane Helene nearly did just that, flooding the town, including Sibelco's works. For a week or so, chip companies fretted about a sudden shortage of the silicon they needed to make semiconductors.

But Sibelco managed to get its machinery up and running within a few weeks. Everyone has now forgotten about this critical link in the global economy – until the next time something goes wrong.

Most major nations around the world have spent decades quietly building up lists of critical minerals. Some are necessary for technology – to make batteries, semiconductors or electric motors. Some are important for construction, others for defence. Some, like rare earth metals, go into more or less everything.

But, as the recent trade spat between the US and China has underlined, most Western countries have failed to turn these lists into physical results. In some respects, this seems almost inexplicable. If these metals are quite so important, why on earth is the US, or for that matter Britain, relying so much on China?

It's not as if they need to – especially America, which has far richer resources near at hand than its rival superpower. There are richer reserves of rare earths in California than in China – but they mostly lie untouched.

To understand why you need to remember two things.

First, blasting rocks out of the ground and turning them into metals is a dirty business, producing plenty of carbon emissions, not to mention other airborne nasties. Refining rare earths produces especially noxious side-products. So most Western nations have been happy to outsource it to countries with fewer environmental qualms (and less pressing Net Zero targets).

Second, despite how exotic this all sounds, in practice the rewards for mining and refining critical minerals have long been rather disappointing. Metals companies go bust with metronomic regularity. And in part this comes back (yet again) to the fact that China has long controlled the market – and competing with China on price is a mug's game.

Back to the Hemerdon mine in Devon and its tungsten.

In theory, this place should be one of the most important suppliers of this critical mineral. When I visited, we drove to the bottom of the open pit, where I picked up a heavy lump of rock flecked with dark spots – tell-tale signs of raw tungsten.

Few other sites have as much of the metal as this place. In theory, it could catapult Britain from zero to being one of the world's biggest tungsten exporters. But right now, it is essentially just a big hole in the ground.

The last company attempting to make a go of the mine went bust a few years ago, leaving an empty site with millions of pounds of equipment and a large, mostly empty 'tailings' dam, which was where the waste was supposed to go (that's what lurks behind the big mound you can see from the road).

Indeed, the only other times this place has ever run for more than a few days was during the two world wars, when it provided the tungsten and tin that helped Britain fight Germany. This time around, Europe is hoping British tungsten could help it wage economic war against other nations.

Now, there's a new company, Tungsten West, hoping for better luck. It says it could get drilling in a matter of months. Last month the European Commission designated it as a 'Strategic Project' for critical materials.

But in practice, it still faces the same challenges. If China rations tungsten exports, this place becomes all-important. If China swamps the market, it is potentially unviable.

Having essentially ignored this stuff for years, even as other nations were building up their stockpiles, Britain is now belatedly trying to catch up – but progress is slow. A critical minerals strategy was due to be published in the spring but is now, I'm told, expected 'very soon'. The question is whether it is all too little, too late.

As the world slides into trade and conventional war, those who control these materials may end up controlling our future.

Ed Conway is economics editor of Sky News and author of Material World