Critical Materials Atlas
Method · value vs volume

Real concentration, or just a price effect?

Trade value is price times quantity — so a rising value-concentration can be a price story, not a who-ships-the-tonnes story. Here every concentration is computed in both value and physical volume (tonnes). Where the two diverge, the value figure is partly price.

Where a material’s value-share sits above its volume-share, the apparent concentration is partly price, not tonnage — lithium is the textbook case: its value exploded in the 2021–22 price spike while tonnage barely moved.
How it’s computed

For each material and year I compute the export Herfindahl and China’s export share in value (USD) and in volume (metric tons, from BACI quantity, ~94% coverage), 2002–2024. When value-HHI sits above volume-HHI — or value-China-share above volume-China-share — a high-priced producer or material is weighing more in dollars than in tonnes.

Caveat: ~6% of flows lack reported quantity (the volume series is computed over reported-tonnage flows); BACI quantities are partly estimated. Computed by build_vq.py.

Material: export concentration (HHI) & China share — value vs volume

Implied unit value (price)

Implied price = export value ÷ tonnage (USD/tonne), derived from the trade data itself. China vs the rest of the world: where China's $/tonne sits above the rest, it is exporting the higher-value processed form rather than ore — which is precisely why its value-share can exceed its volume-share. (Unit values from trade data are noisy — quality/product mix varies — so read trends, not the exact level.)

Where value overstates concentration (the price effect)

Materials ranked by how much more concentrated they look in value than in volume in the latest year (HHI gap, ×100, and China-share gap). A large positive gap means the value figure is partly price.

Materialvalue HHIvolume HHIprice gap (×100)China value%China volume%

Computed from BACI HS02 + HS17 (value & quantity) → volume.json. Volume = metric tons; value = USD. The dotted line in the chart marks the 2017 HS-vintage join.