Commercial bone china microstructures consist of distinct regions of lath-like (～0.2 * 0.6 * 1 μm) anorthite and spheroidal (1-3μm) β-TCP nodules embedded in a heterogeneous glass along with isolated irregular (≤30μm) α-quartz crystals. The composition and morphology of the phases formed on firing suggest that anorthite crystallised in clay relicts by reaction of metakaolin with CaO, β-TCP crystallised from decomposition of bone ash, and the liquid formed on vitrification has variable composition depending on the adjacent phases. P_2O_5 was never detected in the glass suggesting that any P_2O_5 that dissolves in the liquid on firing is transient. The cracks sometimes observed in and around β-TCP clusters are likely due to thermal expansion mismatch between β-TCP, anorthite and the glass phase.
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