Relationship between silica and carbonate. (a) Interpenetrating boundaries between silicified domain and host limestone (highlighted in blue). (1) Nodular limestone; (2) dull chert containing remnant limestone structures; (3) vitreous segments; (4) opalescent reflection; (5) residual limestone. Prasville (Eure-et-Loir). (b) Chert − limestone boundaries etched by hydrochloric acid. Moulds of shrinkage cracks like those in limestone nodule N (right) and finely porous texture due to former calcite inclusions; Pécy (Seine-et-Marne).