The triple point andalusite — Sillimanite — Kyanite

The triple point in the Al₂SiO₅ polymorphic system has been determined experimentally; it lies at 6.5±0.5 kb and 595±10° C. This result differs strongly from the data of other experimental investigations on this system; the reasons for this are discussed. The new data given here for the phase boundaries kyanite/sillimanite and andalusite/sillimanite as well as the resulting position of the triple point agree with petrologic considerations based upon both experimental work in related systems and petrographic observations.Herrn Professor Dr. H. G. F. Winkler danke ich für die wohlwollende Förderung dieser Untersuchung, für wertvolle Diskussionen und Ratschläge sowie für die Erlaubnis, die mit Hilfe der Deutschen Forschungsgemeinschaft aufgebauten Apparaturen zu benutzen. Herr Dr. N. D. Chatterjee korrigierte das Englisch des Manuskripts; hierfür sei ihm herzlich gedankt.     

Synthesis of organic matter in the presence of silicate and lime

Rocks from the Mid-Atlantic Ridge were tested for their potential to synthesize sugars from paraformaldehyde, and amino acids from paraformaldehyde and urea at temperatures between 60° and 90°C and reaction times up to 96 h. All rocks were freed from organic contaminants by combustion at 750°C. Presence of carbonates in one sample yielded lime (CaO) which initiated formose reaction, and urea-formaldehyde condensations. Pentoses, hexoses and amino acids were formed with yields between 5 and 15%. Presence of silicates leads to polymerization and epimerization. Silicates also act as protective agent and buffer medium. The idea is advanced that lime—silicate systems were actively involved in primordial synthesis of organic matter.     

Why do organisms calcify?

Molecular mechanisms on carbonate and phosphate deposition in biological systems are presented. Focal points of the article are processes which control: (1) the transfer of calcium ions from within the cell to the place where a crystal can nucleate; and (2) the oriented growth (epitaxis) of minerals on organic templates which lead to the formation of shell structures, bones or teeth.