Influence of borate-boron on crystal form of calcium carbonate.

Abstract

The influence of borate-boron on the crystal form of calcium carbonate has been studied ex perimentally.And it has been found that borate ions in a parent solution favor the formation of calcite. This experimental result is in good agreement with the prediction from the trend that chemical species which are more easily coprecipitated with calcite or aragonite favor the formation of aragonite or calcite respectively, because the authors reported previously that borate ions are more easily coprecipitated with aragonite than with calcite.

Behavior of dissolved silica in parent solution at the formation of calcium carbonate.

“…1). Similar phenomena to that of dissolved silica were found for fluoride, chloride, sulfate, phosphate and borate (KITANO, 1962;KITANO and OKUMURA, 1973;KITANO et al, 1975KITANO et al, , 1978cKITANO et al, , 1978dKITANO et al, , 1979. That is, the presence of fluoride, chloride, phosphate and borate in a parent solu tion favors the formation of calcite and the presence of sulfate favors that of aragonite, although the former species in a parent solution are more easily coprecipitated with aragonite The mechanisms for these facts remain unclearr to be disclosed.…”

Abnormal behaviors of copper (II) and zinc ions in parent solution at the early stage of calcite formation.

“…The dried precipitates were used for the identification of crystal form of calcium car bonate with an X-ray diffractometer (KrrANO et al, 1968(KrrANO et al, , 1971(KrrANO et al, , 1975(KrrANO et al, , 1978a(KrrANO et al, , 1978b(KrrANO et al, , 1978c(KrrANO et al, , 1978d(KrrANO et al, , 1979a(KrrANO et al, , 1979b; KITANO and OKUMURA, 1973 shows that the value of KZn (distribution coef ficient of zinc between solution and calcite) at the early stage of carbonate precipitation was measured to be very low in the parent solutions containing 0.3 and 0.5 mg/l of zinc ions and to be very high in the parent solution containing 0. The present authors clarified that various inorganic ions and orgnaic compounds dissolved in a parent solution sometimes control the crystal form of calcium carbonate precipitated from the solution (KITANO, 1962;KITANO et al, 1969KITANO et al, , 1976KITANO et al, , 1978cKITANO et al, , 1979aKITANO et al, , 1979bKITANO and OKUMURA, 1973) ion, which are smaller in ionic radius than cal cium ion, favor the formation of aragonite and hinder that of calcite; but divalent metal ions such as strontium ion and barium ion, which are larger in ionic radius than calcium ion, favor the formation of calcite and hinder that of aragonite (KITANO, 1962;KITANO et al, 1968KITANO et al, , 1969. (KITANO et al, 1968).…”

Gastropod nacre: Structure, properties and growth — Biological, chemical and physical basics

“…The high magnesium concentration of the extrapallial fluid is of interest: at about 50-60 mM it is 5-6 times higher than the calcium concentration. In precipitation assays, such high magnesium/calcium fractions were found to favour aragonite growth [143] and to delay the onset of precipitation [144]. Nevertheless, it seems unlikely that shell growth depends on the detailed ionic composition of the extrapallial fluid, considering the organism's ability to induce the growth of different shell layers containing different CaCO 3 polymorphs in close proximity simply by changing the type of organic matrix secreted.…”