Which Intergovernmental Panel on Climate Change factors apply if a clay carries iron, manganese or magnesium carbonates, not just limestone?

Table 2.1 of the Intergovernmental Panel on Climate Change (IPCC) gives tonnes of carbon dioxide (CO2) per tonne of carbonate: magnesite 0.52197, siderite 0.37987, rhodochrosite 0.38286 and ankerite 0.40822 to 0.47572. The ceramics text also names witherite, which Table 2.1 does not list.

Table 2.1 factors

All assume 100 percent calcination. The ankerite range assumes iron, magnesium and manganese are each present in amounts of at least 1.0 percent.

• Calcite, CaCO3: 0.43971
• Magnesite, MgCO3: 0.52197
• Dolomite, CaMg(CO3)2: 0.47732
• Siderite, FeCO3: 0.37987
• Ankerite, Ca(Fe,Mg,Mn)(CO3)2: 0.40822 to 0.47572
• Rhodochrosite, MnCO3: 0.38286
• Sodium carbonate, soda ash: 0.41492

What the ceramics text names

The guide says: "CO2 emissions result from the calcination of the raw material (particularly clay, shale, limestone, dolomite and witherite) and the use of limestone as a flux." Witherite is the mineral form of barium carbonate (my note), and Table 2.1 has no row for it. Using the same method as the glass batch extras page, barium carbonate comes to 0.2230 tonnes of CO2 per tonne. That is my arithmetic, not an IPCC figure.

When the extra species matter

The guide says the Tier 1 method assumes only limestone and dolomite. For Tier 3 it says it is important that all carbonate inputs are considered, and the factor is the weighted average of each carbonate's factor.

What to ask the clay supplier

• An assay that names the carbonate species, not only a total carbonate figure.
• If it shows iron, manganese or magnesium carbonate, weigh each at its own factor.
• The date of the sample and the pit it came from, so the assay can be tied to the months of clay it covers.

500 tonnes of clay with an assay by species

• Calcite 3%: 15 tonnes x 0.43971 = 6.596 tonnes of CO2
• Siderite 1%: 5 tonnes x 0.37987 = 1.899 tonnes
• Magnesite 0.5%: 2.5 tonnes x 0.52197 = 1.305 tonnes
• Total: 9.800 tonnes, reported as 9.8
• The 10% default on the same clay: 50 tonnes x 0.44535 = about 22 tonnes

The percentages are example numbers, not from any real clay.

What Senseible does here

Senseible reads fuel invoices and electricity bills into monthly records, so the fuel and power lines of a furnace or kiln are on file. In the self-serve product it does not read clay assays, so the species and their tonnes come from your own lab reports.

• Process CO2 for clay products without an assay
• Default against carbonate-by-carbonate check
• Magnesite calcination CO2 per tonne
• Glass batch extras beyond soda ash

Sources: IPCC, 2006 Guidelines, Volume 3, Chapter 2: Mineral Industry Emissions

Last reviewed 2026-11-06. Quotes and figures are from the 2006 IPCC Guidelines, Volume 3, Chapter 2. The 2019 Refinement was not checked for this page; check it if a buyer names it. The barium carbonate factor is the page's own arithmetic.