Diatoms organic

Corrosion products metal oxides silt alumina diatomic organisms and their excrement of various colours Nitric acid, sulphamic acid, citric acid, phosphoric acid, complexing agents (EDTA, NTA), or sodium polyphosphates (<4% by wt <60°C)... 

Claverie P 1978 Elaboration of approximate formulas for the interactions between large molecules applications in organic chemistry Intermolecular Interactions From Diatomics to Biopolymers ed B Pullman (New York Wiley) p 69... 

The modihed neglect of diatomic overlap (MNDO) method has been found to give reasonable qualitative results for many organic systems. It has been incorporated into several popular semiempirical programs as well as the MNDO program. Today, it is still used, but the more accurate AMI and PM3 methods have surpassed it in popularity. 

PM3, developed by James J.P. Stewart, is a reparameterization of AMI, which is based on the neglect of diatomic differential overlap (NDDO) approximation. NDDO retains all one-center differential overlap terms when Coulomb and exchange integrals are computed. PM3 differs from AMI only in the values of the parameters. The parameters for PM3 were derived by comparing a much larger number and wider variety of experimental versus computed molecular properties. Typically, non-bonded interactions are less repulsive in PM3 than in AMI. PM3 is primarily used for organic molecules, but is also parameterized for many main group elements. 

At the end of a brief life, the diatom settles to the bottom of the body of water where the organic matter decomposes, leaving the siliceous skeleton. These fossil skeletons, or fmstules, are in the shape of the original diatom plant and have designs as varied and intricate as snowflakes. Examples are shown in Figure 1. 

The Onnagawa Formation conformably overlies the Nishikurosawa Formation and is composed of siliceous shale and shale. The rocks are characterized by organic-rich laminated diatomaceous deposits, siliceous microfossils, and fish bones, while foraminiferal fossil is poor in amounts. The total thickness is about 3(X) m. The age of base of the Onnagawa Formation is estimated to be 12.9 Ma based on diatoms (Koizumi and Matoba, 1989). The age of the top of the Formation is 5.8 Ma. 

Simoneit, B.R.T., Philip, R.P., Jeden, P.D. and Galimov, E.M. (1984) Organic geochemistry of Deep Sea Drilling Project sediments from the Gulf of California - Hydrothermal effects on unconsolidated diatomic ooze. Org. Geochem., 17, 173-205. 

Diatoms (unicellular organisms in water) build their highly symmetrical skeletons out of silica. 

M Diatoms constitute a family of unicellular microscopic algae whose cell walls consist of two boxlike parts which contain silica. They are an important source of food for all kinds of marine organisms. 

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