mineralogy

[Eng. mineral, and Gr. logos =a discourse, treatise; Fr. minéralogie; Ital. & Sp. miner alogia.] Nat . Hist .: A science treating of those natural inorganic products of the earth which po e definite physical and chemical characters. Its objects are to point out the various means to be adopted to ascertain the chemical composition and physical characters of inorganic substances, to determine their specific relations, to examine into their modes of occurrence, and their a ociations, with a view to establishing a systematic cla ification. raspar to have been known from very early times; but little or no progre , however, seems to have been made toward establishing any well-defined characters by which they could be recognized, till in 1669 Nicol a us Steno, a Dane, made the discovery that in crystals of quartz the angles of inclination of adjoining faces were constant, and that the number of faces and their grouping, notwithstanding variations in size, were always the erty of Iceland Spar was observed. In 1672, quartz, which had been already designated by the Arabians crystal (clear ice), was shown by Robert Boyle to be heavier than an equal bulk of water by more than two to one, ice being bulk for bulk lighter than water. In 1772 Romé de l'Isle announced that the various shapes of crystals of the same product were intimately related. He showed that all the forms then known could be derived from one of six, which he called primitive forms. The Abbé Haty in 1784 discovered that ten forms, including the six of de l'Isle, could be produced from various minerals by cleavage, and that these must be the true primitive forms. Hañy also propounded a theory of the structure of crystals, as to the relations of the secondary planes to those of the primitive form. Prof. Wei , of Berlin (1809-1815), established fundamental lines, which he called axes, and to which he showed how all the primitive forms and secondary planes were related. Subsequently, though independently, Mohs (1820-1825) arrived at a division of crystals into four systems of crystallization which coincided with the four axial groups of Wei . He also announced two other systems of crystallization, in consequence of more precise measurements being obtainable by the use of the reflective goniometer. The discovery by Malus in 1808 that a ray of ordinary light reflected at a certain angle from a gla plate po e ed the same properties as that which emerged from Iceland Spar, enabled Brewster in 1819 to point out the intimate relation which existed between the cleavage form of a mineral and its action upon light. Brewster's cla ification of crystals on optical grounds agreed with that of Wei and Mohs on geometrical ones, with the exception of two of the systems. The existence of the two additional systems of crystallization formerly announced by Mohs was, however, now established through their difference in optical characters from the other systems. Thus, six natural systems of crystallization are shown to include all po ible crystal forms. The early attempts at cla ification were very vague, and were founded on supposed external differences, being divided into Earths, Stones, and Metals. Cronstedt's E ay (1758) was the first foreshadowing of a principle in a system of cla ification. The earths he cla ed as Calcareous, Siliceous, Argillaceous, and so on. Werner's last system, published in 1817, after his death, divided fo ils (as minerals were then called) into four cla es: viz., Earthy, Saline, Combustible, and Metallic. The system of Hany (1801), like that of Werner, was a mixed one, but it was the first to direct attention to the importance of crystallographic form to a system of cla ification. In 1816 Berzelius published a system founded on the view that all chemical compounds consisted of an electro-positive and an electro-negative part, the former being the metal and the latter the acid. The dis covery of isomorphism by Mitscherlich eventually rendered this system unworkable.