CRYSTALLIZATION OF RHOMBOHEDRAL PLATELETS IN A RECENT PORCELANEOUS FORAMINIFERAL TEST

Observations were carried out on a deposit located on a porcelaneous t est of Quinqueloculina cf seminula (Foraminifera). They provide new in formation on the mechanism of mineralization in porcelaneous tests. Th is deposit is made of an accumulation of needles, deposited by the Gol gi vesicles. Each needle is constituted by a row of crystallites. The superficial needles are included in a thin layer of amorphous organic matter (mucopolysaccharide or acidic glycoproteins?). Inside this matt er, the crystallites reorganize and new crystallites are formed, arran ging in rows. A partial transportation of material to the contact poin ts between the crystallites leads to a smoothing of the surface of the rows. Neighbouring rows progressively become coalescent and the smoot hing continues, ending in the formation of roughly rhombohedral platel ets. Our observations show that the biomineralization may have the sam e processes as some of non-biotic mineral formation where the complexi ty of crystallite assemblages depends on available energy. The biologi cal activity would consist in i) creation of a confined space where th e crystallization is possible, ii) morphological control of the minera lization, and iii) control of the composition of the liquid from which the crystallization will take place lion-specific pumps or channels).