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Carbonate-bearing ceramic bodies are frequently used in the manufacture of bricks, roofing tiles, wall and floor tiles, pottery and tableware. During the firing of these bodies, clinopyroxene is usually formed in very small crystals, 1-5 µm in diameter or less. In the literature this phase is generally referred to as diopside, but no quantitative data are available. In order to chemically characterize these ‘ceramic’ pyroxenes, nine industrial products were analysed by XRF and XRD (bulk sample) and SEM-EDS (fracture surface). Quantitative ZAF analyses of pyroxene crystals showed a certain chemical variability: SiO2 35-50%, Al2O3 9-20%, Fe2O3 1-15%, MgO 3-14%, and CaO 16-25%. Sodium, K and Ti are always <1%, while ferrous iron is always <0.2% in the bulk sample. Overall, ‘ceramic’ clinopyroxenes present wide chemical analogies with ‘fassaite’, e.g. the abundance of aluminium and ferric iron, and the excess ofwollastonite molecules with respect to the diopside-hedenbergite series.

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During the firing of carbonate‐bearing clay bodies, melilite is frequently formed in the form of very small crystals (1–5 μm or less in size). In the literature, this phase is generally called gehlenite; however, no precise composition is available. To achieve a chemical characterization of this “ceramic” melilite, six industrial products have been analyzed via in situ techniques (scanning electron microscopy coupled with energy‐dispersive spectroscopy) and via X‐ray fluorescence and X‐ray diffractometry (bulk sample). Melilite crystals exhibit the following concentration ranges: 29%–41% SiO2, 32%–42% CaO, 10%–19% Al2O3, 2%–7% MgO, and 4%–10% Fe2O3. The Na2O, K2O, and TiO2 contents are almost always <1%, and FeO is always practically absent in the bulk sample. Overall, “ceramic” melilite seems to be actually a solid solution with the following composition range, in terms of end members: 32%–56% gehlenite, 20%–49%åkermanite, plus a significant fraction of ferri‐gehlenite (14%–37%).