Criticality of non-fuel minerals: a review of major approaches and analyses.

The criticality of nonfuel minerals is an emerging research subject that captures both the supply risks and the vulnerability of a system to a potential supply disruption. The significance of material criticality for the mass deployment of sustainable and other key technologies is currently obscured by diverse, often immature, and still evolving methodologies. This review explores why principal studies agree or disagree in designating the criticality of certain nonfuel minerals. We survey the literature and analyze several well documented studies in depth, demonstrating that the platinum group metals (e.g., essential for catalytic reduction of air pollutants), and the rare earth elements (e.g., essential for efficient electricity generation in wind turbines) are frequently singled out as critical, albeit by differing criteria. We also discuss the impacts of methodological choices on the designation of raw materials as critical. The treatment of substitutability, time horizons, and the aggregation level of criticality indicators are shown to be significant in this regard. We determine several important issues that have thus far been largely disregarded, especially the justification of methodological components, and policy responses to criticality designation.