Methods
How multi-year production trajectories, supply concentration scores (`HHI`), and reserve-to-production (`R/P`) ratios are calculated from U.S. Geological Survey tables.
Multi-Year Production Series (2020-2025)
Each annual edition of the USGS Mineral Commodity Summaries reports two years of country-by-country production (a finalized prior year and a current-year estimate). To build continuous 2020-2025 series, we join the world production files from the 2022, 2023, 2024, 2025, and 2026 ScienceBase data releases. When two editions report the same calendar year, the revised reading from the later edition is used.
Herfindahl-Hirschman Index (HHI)
A producing country's share of 2025 world output (0 to 100) is calculated by dividing its numeric production by the published world total. The Herfindahl-Hirschman Index (HHI) sums the squared percentage shares across all listed countries:
HHI = sum( share_pct^2 ) [Scale: 0 to 10,000]
Minerals where the top producer accounts for at least 50% of world output, the top 3 producers account for at least 75%, or HHI is 3,500 or higher are marked as Critical Chokepoints.
Reserve-to-Production (R/P) Ratio
When USGS reports global proven reserves and 2025 world mine production in identical physical units, the implied reserve horizon in years is:
R/P Ratio (Years) = World Proven Reserves / 2025 World Production
Where reserves and production use different physical bases (such as gross chromite ore vs. Cr2O3 content), no R/P ratio is shown.
Withheld ("W") Values & Qualifiers
USGS withholds ("W") certain country or domestic production figures to avoid disclosing proprietary company data. Withheld or missing figures are preserved as reported and are never treated as zero.