Silicon

Material criticality in context

Silicon presents the clearest example in this study of a material whose criticality is unrelated to geological scarcity. As one of the most abundant elements in the Earth's crust, extracted primarily from quartz, it faces no meaningful prospect of global resource depletion. Instead, its criticality stems from the exceptionally high purity required for advanced applications and the limited ability to recover that material once it has entered use.¹³⁸

Silicon reaches its end uses through a hierarchy of increasingly demanding purification stages. Carbothermic reduction of quartz produces metallurgical-grade silicon at roughly 98–99% purity, suitable for aluminium alloys and chemical applications, which together account for most production by volume. Solar photovoltaics require polysilicon at around six-nines (6N) purity, while semiconductor manufacturing requires nine-nine (9N) purity or higher, where even trace impurities render material unusable.¹³⁹ These are not simply different grades of the same product but functionally distinct materials requiring increasingly complex and energy-intensive processing. It is within these purification stages that much of silicon's economic cost, energy burden, and strategic vulnerability are concentrated.

That vulnerability is reinforced by an exceptionally concentrated supply chain. Silicon metal production is dominated by a single country, while polysilicon production is similarly concentrated.¹⁴⁰ Further downstream, wafer manufacturing and associated chemical processing are controlled by a small number of countries, and the most advanced semiconductor fabrication is effectively concentrated in a single firm.¹⁴¹ Silicon's supply chain therefore comprises a series of bottlenecks rather than a single point of vulnerability. The consequences are already evident: disruptions to silicon metal production in late 2021 led to price increases of several hundred per cent within months. Substitution offers little relief, particularly in applications above metallurgical grade, where alternative materials cannot readily replicate silicon’s performance.¹⁴²

The environmental impacts of silicon production are driven primarily by energy consumption rather than land or water use. Carbothermic reduction is highly energy-intensive and, in the dominant producing regions, remains heavily dependent on coal-fired electricity.¹⁴³ The quality of the raw quartz also matters. High-purity deposits are comparatively uncommon, and where beneficiation is required to achieve suitable feedstock quality, the carbon footprint of silica production more than doubles, carrying through to silicon production itself.¹⁴⁴ Further downstream, wafer fabrication has been identified as one of those most resource-intensive stages of semiconductor manufacturing, consuming large quantities of water, energy, and process chemicals. In several major manufacturing regions, water availability has already emerged as a practical constraint on production.¹⁴⁵

Silicon’s role in semiconductors increasingly defines its criticality. Semiconductors have evolved from commercial products into strategic assets underpinning digital infrastructure, while rapid growth in artificial intelligence is placing additional pressure on demand for semiconductor-grade silicon.¹⁴⁶ This intensifies pressure on a supply chain whose constraints are already structural. Recent geopolitical tensions have demonstrated how vulnerable this supply chain can be, with export restrictions affecting key materials and specialty chemicals required for wafer production.¹⁴⁷

Material flows and application structure

The Sankey diagram maps how silicon moves from refined metal through its material streams into applications and final end uses, as of 2020. It is interactive: selecting any stream or application traces the flows connected to it. This is a conceptual visual showing the approximate distribution of silicon across material streams, applications, and end-uses. The diagram also illustrates a defining characteristic of the silicon system. Material flows are dominated by ferroalloys destined for steel and cast iron production, while the semiconductor and solar-grade streams that underpin silicon's strategic importance account for only a small share of total volume.