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(Ammonoidea), a superorder of extinct invertebrates of the Cephalopoda class.
Ammonites lived over the entire earth from the Devonian period through the Cretaceous period inclusively. They had an external, often sculptured, shell of varying shape, divided into a number of chambers by transverse septa. The edges of the septa were usually greatly corrugated; the corrugation increased the strength of the shell. The soft body of the animal was in the last chamber, which terminated in the opening. The remaining chambers were filled with gas and played the role of a hydrostatic apparatus. They were interconnected by a cordlike growth of the soft body—the siphon—with blood vessels which provided a normal gas regime in the chambers. The diameter of the shell was as much as 2 meters.
Ammonites were widely found in the seas and were predators. Some of them swam well, and others crawled for the most part. A total of about 1,500 genera are known, as well as numerous species which quickly replaced one another over the ages. Because of this, the ammonites are one of the most important groups of “leading” fossils. The ammonites are also of interest for elucidating the patterns of individual development (ontogenesis) and its relationship to phylogenesis, since all the parts of the ammonite shell changed greatly in the process of ontogenesis.
REFERENCEOsnovy paleontologii: Molliuski-golovonogie, [vol. 1]. Moscow, 1962.
V. N. SHIMANSKII
ammonium nitrate explosives, explosive mixtures of ammonium nitrate with combustible and explosive substances. Ammonites are secondary (brisant) explosives. Organic substances (wood flour, peat, oil cake, petroleum oils) or inorganic materials (aluminum powder, fer-rosilicon) are used as combustible substances in ammonites. Nitroglycerin and other nitrate esters, trotyl (trinitrotoluene, TNT), hexogon (cyclonite), or PETN (penta-erythrityl tetranitrate) are used as explosives.
The mixtures of ammonium nitrate with combustible substances are called dynammons; those with TNT, amatols; those with aluminum powder and TNT, ammonals; and those with hexogen, aluminum, and TNT, rock ammonites. Mixtures containing considerable amounts of liquid nitrate esters are classified as dynamites. The performance characteristics of the ammonites are heat of explosion, 2.1–8.4 megajoules per kg (500–2,000 kcal/kg); detonation rate, from 1.5–2.0 to 5–6 km/sec; blasting-charge density, 0.8–1.5 g/cm3. The manufacture of ammonites consists in preparing their components (drying, grinding, and screening) and mixing them. The resulting mixtures are packed or used for the production of cartridges.
Ammonites are used in various kinds of open-pit and underground blasting, for charging various types of ammunition (mines, bombs, and shells), and for engineer corps blasting. The advantages of ammonites over other explosives are their high chemical stability and relative safety in production, storage, and handling; disadvantages are their hygroscopicity, low water resistance, and caking tendency.