What makes something a commodity: Key terms, quiz and sources

Understanding Commodities / Module 1: What makes something a commodity Wrap-up

What makes something a commodity: review

Key terms

Commodity: A good traded against a standard description, so that any lot of the stated grade can replace another and a shared market price can form.
Fungibility: The property of being interchangeable unit for unit, so buyers care about grade, place, date and price rather than who produced the good.
Grade (specification): The defined quality a contract refers to, such as 62 per cent Fe iron ore or arabica coffee; different grades can form separate markets.
Delivery basis: The terms that fix where and how a price applies, such as free on rail at the mine or cost and freight at the buyer's port; for bulk goods they can halve or double a price.
Price discovery: The process by which trading reveals a market price that others then use as a reference for their own deals.
Benchmark price: A published reference price, from an exchange, an index or a lead negotiation, against which other contracts are priced with adjustments for quality and location.
Producer price: A take-it-or-leave-it price announced by a few dominant sellers, which changes less often than exchange prices and may hide rationing or rebates.
Clearing house: The body attached to an exchange that becomes counterparty to every futures contract and holds margins, guaranteeing performance.
Soft commodity: In trading usage, a tropical crop such as coffee, cocoa, sugar or cotton; more loosely, any grown rather than mined commodity.
Stocks-to-use ratio: Ending stocks divided by a year's use; a low ratio means supply shocks hit prices hard.
Price elasticity of supply: The percentage change in quantity supplied for a one per cent change in price; low in the short run for mines and tree crops.
Main product, co-product, by-product: A main product's price alone sets a mine's ore output; co-products share that role; a by-product's price has no effect on ore output.
Companionality: The share of a metal's primary production obtained as a companion of a host metal, as measured by Nassar, Graedel and Harper.
Secondary supply: Supply from recycled new scrap (from manufacturing) or old scrap (from products at the end of their life), outside primary producers' control.
Value density: Value per kilogram; low value density makes freight a large share of delivered cost and keeps markets regional or local.
Herfindahl-Hirschman Index (HHI): The sum of squared market shares, from near 0 for a fragmented market to 10,000 for a monopoly; the table computes it across countries.
EU supply risk: The EU's score combining governance-weighted supply concentration, import reliance, trade restrictions, substitution and recycling; 1.0 or more is one of the two tests of criticality.
End-of-life recycling input rate: The share of a material entering EU production that comes from post-consumer scrap.
Reserves and reserve life: Reserves are identified deposits economic to extract today; reserve life divides them by current output and is a working inventory, not a countdown.
Monoeconomy: In Radetzki and Wårell's usage, a country whose leading non-fuel commodity exceeds 40 per cent of its exports.

Try it in the table

Open Gallium and then Aluminum. Gallium shows a 95 per cent by-product share and an HHI of 9,739. Look at who smelts aluminium and where alumina is refined, and explain why a gallium buyer must follow the aluminium industry and Chinese export policy rather than gallium mines.
Open Copper. Compare the mine-output HHI of 1,089 with China's share of refinery output, then check the copper ore trade shares (Chile and Peru as exporters, China as importer). Where does the transformation in form happen, and which stage would you watch for supply risk?
Open Wheat and Cocoa. For each, note how long it takes to add supply and what the stocks figures show. Which market should recover faster from a price spike, and why?
Open Lead, Copper and Lithium and compare their EU recycling input rates (83, 55 and 0 per cent). For each, say whether the rate is limited by collection, by dissipation, or by metal still locked in products in use.
Open Zinc and Lithium. Zinc's reserve life is 18 years and lithium's 128. Using the copper reserve history, explain why zinc is not about to run out, and what the two numbers do tell you.
Open Gold and Diamonds. Gold has a low HHI and a price quoted everywhere; diamonds have no exchange price. List which commodity tests each passes or fails: fungibility, grading, storability and price discovery.

Final quiz

Which feature most fundamentally makes a good a commodity?

Fungibility against a standard specification is the core. Many commodities trade mainly by contract or auction rather than on exchanges, and ownership or costs do not define them.

According to Tilton and Guzmán, what defines a by-product?

A main product's price alone sets ore output and co-products share that role; a by-product is so minor that its price does not affect ore output, which is why its supply hits a ceiling set by the host.

Why did Radetzki and Wårell's 1825 to 1910 fall in New York to Liverpool freight, from 55.1 to 3.5 dollars a ton, matter so much for wheat?

For goods with low value per kilogram, freight is a large share of the delivered price. As it fell, overseas grain undercut European farmers; in Britain home-grown bread grain fell from two thirds of supply in the 1850s to 20 per cent by the 1880s.

Which commodity is the best example of producer-dictated pricing in Radetzki and Wårell's account?

They call the De Beers arrangement for uncut diamonds the example par excellence of producer pricing. Every stone differs, so there is no exchange price.

Cobalt's price rose from 5.40 to 25 dollars a pound after supply from Zaire was disrupted. What happened next, and what does it show?

Short-run demand barely responded, but over several years users substituted. When Zairean output recovered, the price fell back. Long-run elasticities exceed short-run ones.

A tile shows an HHI of 1,089 for copper mining. What can you safely conclude?

The HHI is computed across countries for mine output. China refines about 48 per cent of copper, so concentration differs by stage, and firm-level control can differ from country shares.

What is the end-of-life recycling input rate on a tile?

It measures recycled content in inputs, not collection rates. A material can be well collected yet show a low rate if in-use stocks are growing fast, as Krausmann and colleagues show for materials in general.

Erten and Ocampo's study of real commodity prices from 1865 to 2009 found what?

The declining mean of successive non-oil cycles supports the Prebisch-Singer hypothesis. Oil, by contrast, had a long-term upward trend, interrupted for a time in the twentieth century.

Next module: From ground to market →

Sources for this module

Radetzki, M. & Wårell, L. (2021). A Handbook of Primary Commodities in the Global Economy, 3rd ed. Cambridge University Press. · pdf pp. 15-27, 30, 39-49, 61-62, 104-107, 117-125, 141-151, 203, 228-229, 267-276, 288-294
Tilton, J.E. & Guzmán, J.I. (2016). Mineral Economics and Policy. RFF Press / Routledge. · pdf pp. 16-27, 31, 65-79, 95-99, 178-185, 191-192
Geman, H. (2005). Commodities and Commodity Derivatives: Modeling and Pricing for Agriculturals, Metals and Energy. Wiley. · pdf pp. 13-14, 21-23, 49, 154-155, 159, 162-165
Blas, J. & Farchy, J. (2021). The World for Sale: Money, Power and the Traders Who Barter the Earth's Resources. Random House Business. · pdf pp. 42-43, 62-63, 78-79, 100-102, 111-112
Morgan, D. (1979). Merchants of Grain. Viking Press. · pdf pp. 90, 97-99, 103
Humphreys, D. (2015). The Remaking of the Mining Industry. Palgrave Macmillan. · pdf pp. 123-126
Conway, E. (2023). Material World: A Substantial Story of Our Past and Future. W.H. Allen. · pdf pp. 204-205
Yergin, D. (1991). The Prize: The Epic Quest for Oil, Money and Power. Simon & Schuster. · pdf pp. 37, 1247-1250
Pirrong, C. (2014). The Economics of Commodity Trading Firms. Trafigura. · pdf pp. 4, 6-9
Nassar, N.T., Graedel, T.E. & Harper, E.M. (2015). By-product metals are technologically essential but have problematic supply. Science Advances 1(3): e1400180. web ↗ · pdf pp. 1-6
Graedel, T.E. et al. (2015). Criticality of metals and metalloids. PNAS 112(14): 4257-4262. web ↗ · pdf p. 1
Krausmann, F. et al. (2017). Global socioeconomic material stocks rise 23-fold over the 20th century and require half of annual resource use. PNAS 114(8): 1880-1885. web ↗ · pdf p. 1
Erten, B. & Ocampo, J.A. (2012). Super-cycles of commodity prices since the mid-nineteenth century. UN DESA Working Paper 110. web ↗ · pdf pp. 1, 3-4
European Commission (2023). Study on the Critical Raw Materials for the EU 2023: Final Report. web ↗ · pdf pp. 5-7, 22, 34, 48, 55
US Geological Survey (2026). Mineral Commodity Summaries 2026: Copper, Gallium, Diamond (Industrial) and Appendix C. web ↗ · pp. 72-75, 82-83, 217
USDA (2026). World Agricultural Supply and Demand Estimates, WASDE-676, October 2026. web ↗ · World Wheat Supply and Use
World Bank (2026). Commodity Price Data (Pink Sheet). web ↗ · monthly prices to September 2026
UN Comtrade (2024). HS 2603 copper ores and concentrates. web ↗ · 2024 export and import shares