6o 



Cincinnati Society of Natural History. 



number of furnaces. The only triclinic feldspar noted as accident- 

 ally formed is anorthite recorded by Velain in 1878. 



Nineteen years after Leondard wrote the statement above, the 

 first successful attempt at the reproduction of feldspar was made, 

 when Hautefuille formed orthoclase. He heated at a temperature of 

 900 degrees, a mixture of tungstic acid and a very alkaline silico- 

 aluminate of potash. The resulting products were orthoclase, tri- 

 clinic silico-aluminate of potash, and tridymite. By changing the 

 proportions the two side products disappeared after twenty days 

 heating. The orthoclase crystals possessed the physical and optical 

 properties of the natural mineral. 



By an analogous method with the silico-aluminate of soda, this 

 investigator formed albite. 



By a fusion of the elements, Foque and Levy formed anorthite. 

 (See figure 1,) oligoclase and labradorite. The crystals were usually 

 microlites one millimetre long and twinned alter the albite law. All 

 the feldspars were reproduced by igneous agency, but the more basic 

 ones are the more readily formed. The synthetic work on feldspars 

 has confirmed the theory of Tschermak that the various tri-clinic feld- 

 spars are not distinct species, but they are isomorphous mixtures of an 

 albite (sodium) molecule and an anorthite (calcium) molecule. 



By a fusion of silica, alumina, carbonate of soda, with strontium, 

 barytes, and oxide of lead, Foque and Levy obtained new feldspars with 

 those bases. After their experiments were published, Des Cloizeaux 

 discovered a natural barytes feldspar (hyalophane) with properties 

 like the artificial one, but so far no lead or strontium feldspar has 

 been noted in nature. 



The two most important minerals in the alkaline series of rocks 

 are leucite and nepheline. (See figure 1.) The former was reproduced 

 in 1880, by Hautefeuille, by a fusion of a mixture of silica, aluminate 

 and vanadate of potash at 800 degrees temperature during twenty-five 

 days. The same action on the aluminate of soda with an excess of 

 vanadate of soda gave crystals of nepheline. 



In the sedimentary rocks the more important minerals are calciie 

 and dolomite. Calcite was first formed by James Hall, in 1801. This 

 experiment was repeated by Bischof and also by Rose, in 1837. The 

 latter proved that the same action produced crystals of calcite and 

 aragonite (orthorhombic form) which were formed at different parts of 



