In the mid of the 19 th century, it became obvious that mineralogical concepts based only on qualitative observations were not sufficient anymore to study minerals and crystals. The ideas of Haüy, that more or less every chemical substance is only represented by one crystal structure, which itself is inferred from one single primitive structure, had to be revised. The discovery of transition phases between mineral species confirmed that the general organization of mineral and crystallographic groups had to be redefined. The main focuses of mineralogy research in the second half of the 19 th century were the questions of paragenesis, mineral formation and the building of the inner structure of crystals. The quantitative approach generalized and progressively replaced observations and deductions in all aspects of mineralogical studies. Scientists tried to focus on exact measurements of crystallographic structures, precise determination of physical parameters and accurate chemical analyses of minerals.
F. A. Breihaupt (1791-1873) postulated in 1849 the theory of paragenesis, where he summarized the occurrence of special minerals and their modes and conditions of formation. His work influenced many fields of the geosciences. The quantitative methodology was strongly advocated for example by G. Rose (1798-1873) in his book, written in 1852 but still valid today, titled "Krystallo-Chemische Mineralsystem". His work led to the systematic organization of mineral based only on their chemistry and crystallography. Of particular importance to document the thermodynamic properties of minerals, was the discovery in 1876 by W. Gibbs (1839-1903) of the "phase rule". It helps to predict, in an enclosed system and known elemental composition, which mineral phases should form under specific conditions of pressure and temperature. Another key discovery which is today probably one of the most commonly used technique in the geosciences was the introduction by W H. C. Sorby (1926-1908) in England of the method of transmitted light microscopy to investigate thin sections of minerals and rocks. In 1874, another British, H. Miller (1801-1880) constructed the two circle reflecting goniometer, which greatly eased, sped up and improved the measurement of crystal faces. Miller was already famous for his concept of Miller indices to identify crystal faces whichy he developed in 1839. In 1895, the German physicist Wilhem Conrad Roentgen discovered that cathode ray tube emitted a mysterious radiation which penetrated black paper. This radiation later called X-ray is now widely used to characterize and identify crystal structures, using the X-ray diffration method first developed by Friedrich, Knipping, and von Laue in 1912. The late 1800 also saw the discovery of radioactivity by French chemist Henri Becquerel . By placing uranium-rich minerals wrapped in black paper on a photographic plate Becquerel realized that they emitted radiation continuously fogging the plate. This discovery which Becqurel presented at the Academie des Sciences in Paris in 1986 very much influenced chemistry, physics and mineralogy in the 20 th century and formed the basis of the work of Marie and Pierre Curie.
Crystal physics
Among the scientists of the second half of the 19 th century, which worked on the physical crystallography, especially elasticity, density, electricity were E. Mallard and T. Liebisch. Mallard focused on optical characteristics of minerals and explained in details abnormal optical phenomenon in crystals in his seminal paper "Explication des phénomènes optiques anormaux, que présentent un grand nombre de substances cristallisées" published in 1876. In parallel with the optic light investigations, V. von Lang in Vienna and E. Jannettaz in Paris analyzed thermal conductivity in crystals. At the same time, A. Fizzeau in France and L. Fletcher in England worked on thermal expansion rates in crystals. Many scientists, among them G. Hankel in Leipzig focused their attention on electrical properties of crystals. In 1880, J. and P. Curie discovered that if pressure is exerted at the end of a crystal polar axis a negative charge is produced at one end and a positive charge at the other end, this phenomenon is called piezoelectricity.
Crystal geometry
On of the most important scientist in the second half of the 19 th century in the field of crystal geometry was the French August Bravais (1811-1863). He developed the theory of crystal lattices (network, space lattice), named after him and published them 1850 in "Memoire s. l. systémes formés par des points distributés régulièrement sur un plan ou dans l´espace". He proved, that only 14 different lattices are possible. Bravais work had a great influence on crystallography. In his book "Traité de Cristallographie géometrique et physique" from 1874, E. Mallard developed the principles of modern crystallography, based on the Bravais theory. In Germany, L. Sohnke worked on this theory, which was presented in 1879 in his thesis "Entwicklung der Theorie einer Kristallstruktur". He postulated that 65 regular crystal lattices to explain symmetry, cleavage as well as the grade of symmetry (normal symmetric or lower grade of symmetry). Based on his work, the Russian mineralogist F. Fedorow (1890) -who had already invented the universal stage to improve microscopic investigations-, and the German mathematician A. Schönflies (1891) developed independently the general theory of internal symmetry and order within crystals which was later very much used in X-ray crystallography. Both showed evidence for 230 different types of structure, based on rotation and reflection of the simple crystal symmetry classes. In England the physicist Lord Kelvin worked on understanding close packing system in crystals.
Chemical crystallography
The amount of chemical investigations on minerals increased enormously at the end of the 19 th century. In 1846 E. de Beaumont (1798-1874) published an overview of the frequency of chemical elements in the Earth's crust. Even the growth and dissolution behavior of minerals were investigated (F. Leyboldt, V. v. Ebner, F. Becke). In 1890, A. Verneuil (1856-1913) was able to synthesize for the first time the mineral ruby. The most extensive compilation of mineral deposits and investigations of special minerals can be found in C. Hinze´s (1851-1916) "Handbuch der Mineralogie" and in James D. Dana (1813-1895) book "A system of Mineralogy". Both of these books are still widely used today.
Regional mineralogy
During the 19 th century regional descriptions of mineral deposits evolved in parallel with investigations of the theoretical problems in mineralogy. Compilations containing vast information about mineral characteristics, form, structure, type of occurrence etc were published in various countries. The late 19 th century industrial revolution demanded abundant raw material of whole sort. Precise mineralogical knowledge played a key role in mining and metallurgical developments as well as in the chemical industry. A brief selection of the most important papers of the second half of the 19 th century is listed below, they illustrate the need to summarize the mass of observations accumulated during this period on mineral descriptions and analyzes.
Bibliography
Germany
August Frenzel (1842-1902) &endash; "Mineralogisches Lexikon für das Königreich Sachsen" 1874
O. Lüdecke (1851- 1910) &endash; "Die Mineralien des Harzes" 1896
H. v. Dechen - "Die nutzbaren Mineralien und Gebirgsarten im deutschen Reiche" 1873
F. Besnard &endash; "Die Mineralien Bayerns" 1854
F. Klockmann "Lehrbuch die Mineralogie" 1892
Austria/Hungary
J. F. Vogl - "Gangverhältnisse und Mineralreichtum Böhmens" 1856
M. J. Ackner - "Die Mineralogie Siebenbürgens" 1885
Einen zusammenfassenden Überblick geben V. v. Zepharovich und F. Becke in dem dreibändigen Werk: "Mineralogisches Lexikon für das Kaiserthum Österreich" 1859, 1873 und 1891
Italy
G. Jervis "I tesori sotterranei dell´ Italia" 1873 &endash; 1889
France
Lacroix "Minéralogie de la France" 5 volumes 1893-1913
Spain/Portugal
C. Tenne und S. Calderón &endash; Die Mineralfundstellen der Iberischen Halbinsel 1902
S. Calderón &endash; "Los Minaralos de España" 1908
Great Britain
K. Ph. Greg und W. G. Lettsom &endash; "Manual of the mineralogy of Great Britain and Ireland 1858
Russia
N v. Kokscharow &endash; "Materialien zur Mineralogie Rußlands" 11 Bände1853 &endash; 1891
James D. Dana (1813-1895) published "A System of Mineralogy", where a compilation of all minerals outside Europe can be found.
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