Inner structure of the thick carbonate scale (inner part of the sample G-03). The growth direction is marked by yellow arrows. (a) The scale precipitation begins with a thin (<500 μm) compact lamina composed of limpid, tightly packed fibrous or bladed crystals (F zone), following a relatively compact dendritic–botryoidal zone (B1 zone). (b) Dendritic and feather-like calcite generation in the B1 zone. (c, d) Spherical growth zones made up of dendritic and bladed crystals and subdivided by a thin, bright luminescent film. Note: B1/B2 boundary (an intermittent brownish stained layer) separates annual operational rhythms. Red arrow indicates a very thin brownish stained layer without luminescence. (e) Feather-like dendrites in the porous B2 zone. (f) Contact of a limpid, tightly packed zone, made up of fibrous crystals and a fine, tightly packed zone with turbid crystals in the compact B3 zone. Abbreviations: PPL = plane polarized light; CL = cathodoluminescence.