Nineteenth Century Amorphous Calcium Carbonate

Abstract

The work of the English anatomist George Rainey is compared with that of the Dutch naturalist Pieter Harting. While the latter is regarded as a pioneer in biomimetic inorganic crystallography for precipitating unusual crystallographic forms that mimic the products of living organisms, the work of Rainey largely has been forgotten. In fact, Rainey first prepared amorphous calcium carbonate, a material that can be molded by organisms to form biogenic crystals. Rainey's extensive experimentation with amorphous calcareous bodies observed in a variety of organisms was at one time considered a significant and pioneering chapter in inorganic chemical morphogenesis and it should reclaim some of its former assessments. Rainey's interpretations of crystal form and the effects of gravity on crystal growth mechanisms, however, are historical curiosities that should be left behind, except to the extent that they show how the efforts of an individual may appear diminished by the dynamic process of consensus building in science. Harting also prepared amorphous calcium carbonate, but more than a decade after Rainey. While Rainey was a quiet scholar with steady habits, Harting was a statesman, a champion of the down-trodden (albeit with prejudice), a popular educator, a temperance advocate, and a sci-fi novelist, in addition to being a professor. Harting's public life may account for his outsized place in our collective memory. Rainey's synthesis of amorphous calcium carbonate in the presence of gum arabic was repeated in a modern setting. Microspheres were characterized by scanning electron microscopy, established as hollow by X-ray microtomography, and were shown to have the composition of calcium carbonate by energy dispersive X-ray analysis. They were amorphous by powder X-ray diffraction.

Figure 1

Charcoal portrait of George Rainey by his son, William, as reproduced in ref (74). This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

Figure 2

Detail of Rainey’s Figure 6 of an oyster shell (ref (59)). b marks globules of amorphous carbonate of lime. c marks distinct bodies “in which a cross can be seen with polarized light.” This material has been provided by King’s College London. The original may be consulted at King’s College London.

Figure 3

“Spherolith formation of calcium carbonate by layering of gum acacia showing the growth of spheroliths by aggregation. (×110.) (Rainey’s experiment reproduced, 1962).” From Figure 6 of ref (75). Reprinted with permission 5896480774933. Copyright 1962 British Medical Journal Group.

Figure 4

Rainey’s amorphous calcium carbonate (ACC) spheres. I. Synchrotron X-ray computer tomography (CT) of the reaction tube containing Ca-malate and K₂CO₃ gum arabic [yellow arrows indicate forming ACC spheres]. II. Nanosynchrotron-X-ray CT of a single ACC sphere. III. Scanning electron micrograph of a single ACC sphere. IV. Energy dispersive X-ray (EDX) spectroscopy of ACC sphere [see yellow spot for location in III]. V. X-ray diffraction of the ACC spheres.

Figure 5

Oil painting of Pieter Harting by Johan Heinrich Neuman (1819–1898) (Professoren van de Universiteit Utrecht). Universitätsmuseum Utrecht. This work is in the public domain in its country of origin and other countries and areas where the copyright term is the author’s life plus 100 years or fewer.

Figure 6

Giant squid fragment reproduced from ref (117). This work is in the public domain in the United States because it was published (or registered with the U.S. Copyright Office) before January 1, 1929.