MINERALOGY. 539 MINERALOGY. bles, and ashostns talnii's. (4) Abrasives, em- bracing diauioniU. einciy, garnet, and imartz sanil. (.5) tirapliie materials, embracing elialk, graphite, pencil stone, lithograpliie limestone, etc. (G) Pigments, iueluding minerals ground for paints, and paint adulterants. (") Fer- tilizers, represented by the lime phosphates^ marls, and land plaster. (S) Mineral fuels, in- cluding coal. |)etroleum, and natural gas. The use of certain minerals for gems is probably of ery ancient origin. The extreme hardness of the diamond, sapphire, ruliv. emerald, chrysobcryl. and otlicr ]ireci(jus stones protects them from iiijirv and renders them cajiable of being highly )iolished. Synthetic Miner.logy. Almost all of the important minerals have been successfully l)ro- dneed artificially, and much light has been thrown upon the formation of natural minerals in this way. The methods applied to this line of re- search involve in the majority of cases a fusion at a high heat for ,a long period. In a number of instances artificial minerals have been acci- dentally produced in the ccnirse of various metal- lurgical operations, and the interiors of retorts and furnaces often furnish interesting examples of this phase of mineral genesis. In point of economic imiiortance these experiments, though interesting, have not as yet achieved a marked degree of success in the production of gems, and although both the ruby and the diamond have been made in this way, the crystals in every case have been comparatively small. ANALV.SIS OF Jli.N'ERALS. The determination of minerals is largely a question of experience gained by the stud}- of large and varied collec- tions of specimens. The eye becomes trained by practice to recognize crystallizations even in dis- torted and imperfectly exposed forms, to asso- ciate certain colors, lustre, and structure with definite species, and to associate certain min- erals with certain rock matrix. Several phys- ical properties are of considerable aid in identifying questionable specimens, as, for ex- ample, the color of the powdered mineral as shown by rubbing it on unglazed porcelain, the approximate relative hardness as determined by scratching the specimen with a knife point, and the relative weight as roughly determined by weighing the specimen in the hand. These rough determinations which are of particular value as field methods may be supplemented, with the addition of some siniide and portable apparatus, by determinations of s(dubility and fusibility. A more detailed examination of the composition of a mineral involves recourse to the blowpipe analysis. Some idea of the results obtained by this foiin of analysis will be gained by an exami- nation of the accompanying plate, which shows the reactions obtained from some of the fusible metals by heating their compounds with suitable (luxes on charcoal and plaster supports. The coatings of iodides arc produced by using a flux composed of two parts sidphur and one part each of potassium bisul])hatc and potassic iodide. Re- actions for iron, copper, manganese, nickel, co- balt, chromium, and otlier metals are obtained by dissolving small portions of their compounds in hot beads of borax or microcosmic salt and sub- jecting the resulting fusion to the oxidizing and reducing action of the blowpipe flame. The color imparted to the blowpipe flame serves as a test for compounds of calcium, strontium, lithium. Vol, Xlll.— a5. barium, sodium, and other elenu'nts. These tests as well as others of similar nature merely an- nounce the jjrescnce or abseiu'e of an element ; the relative amcmnt when required must be deter- mined by a systematic quantitative analysis. Ili.sTOHY. Although a few mineral species were known to philosophers at an early date in the world's history, it was not until the dcvelojiment of chemistry from alchemy in the sixteentli cen- tury that savants approached the subject of mineralogical knowledge in the true spirit of scientific investigation. As a natural outcome of the comparatively advanced state of mathe- nuitical knowledge at the period of this scientific awakening, the subject of crystallization early developed a marked imjiortance. In 178.3 De- lisle, with the aid of a primitive fomi of goni- ometer, measured tlie interfacial angles of a num- ber of crystals and established the law of con- stancy of interfacial angles. The Abbt> Haiiy about the same time developed a theory corre- lating the internal structure of crj'stals with tlieir outwai'd form. He practically formulated the law of rational indices which constitutes the corner-stone of crystallography. Haiiy was fol- lowed by liausmann with his application of spherical trigonometry in 180.3, Weiss with a development along purely mathematical lines in 1814, ilohs with a division of crystals into six systems in 18"22, Xaumann in 1823, and W, H. Miller in 1839. In recent years the science has made vast strides, and new methods and lines of research are being constantly developed. Our knowledge of the science of mineralogy is con- stantly enriched by the discovery of new species, v.'hile mining and quarrying operations are con- tinually bringing to light new and interesting crystalline forms and varieties of well-known minerals. Research in physical mineralogy is being ex- tended, notably in Germany, along a nundjer of lines, and from time to time valuable additions are made to our store of knowledge by careful and exhaustive studies of the optical, thermal, and electrical properties of certain mineral spe- cies. A method by which the symmetry of crys- tallized minerals may be investigated has been developed by Baumhauer. Beck, and others. This method depends upon the development of minute angular cavities upon crystal faces by means of the interrupted action of some dissolving medium. The symmetry of these pits, which are known as etch figures, conforms to the crystallograjihic symmetry of the mineral experimented upon. Of a similar nature in their bearing upon the ques- tion of crystal structure are the percussion fig- ures and solution planes which have been made objects of special study by several authors. Tlie artificial formation of minerals opens another line of research upon which much valu- able work has been done by I)aid)ree, Fouque. Michel Le--y, Fricdel, Bourgeois, Mevmier, and others. BiBLiOGR.PHY. Among valuable works on gen- eral mineralogy- may bo mentioned: Bauerman, Trxt-Book of Dcscriptire Mineralogy (London, 18S4) : .1. D. Dana. .S'v«'cm nf MinVraloqn (fith ed.. New York. 1802) ;' E. S. Dana, Texi-Bool; of Miiirralofiif (New York, 1808) ; Des Cloizeaux, }fnni(cl de min/rnlogic, with atlas (vol. i., Paris. 1802: vol. ii.. parti., 1874) : Tschermak, Lehr- huch der Minernlofiic (Vienna. 1885). Of a rather more elementarv nature but of consider-
