27 s JP. D. Adams — MeliUte-ljearing Rock. 



An attempt was made to separate 

 the melilite from the ground mass of 

 one of the freshest and most coarse 

 g r a i n e d specimens by means of 

 heavy solutions but it was found to 

 be impossible to do so, the average 

 melilite individuals being too small 

 and the mineral being impure on 

 account of the presence of inclu- 

 sions and decomposition products. 

 The melilite is well seen only in 

 sections of the fresh rock, when the 

 Fig. 2 Melilite showing "peg rock ig decomposed to any consider- 



biotite, magnetite and apatite, able extent the mineral is replaced 



by alteration products and no longer 

 easily recognizable. When a portion of the groundmass is 

 finely powdered and boiled for a short time with hydro- 

 chloric acid a slight gelatinization can be observed suffi- 

 cient to cause the powder to adhere to the sides of the 

 tube but not sufficient to make a jelly. When a section is 

 treated with hydrochloric acid and then with fuchsine the meli- 

 lite is seen to be distinctly stained. 



Wepheline. — In addition to the melilite and in much smaller 

 amount, there is in many sections a clear colorless mineral 

 occurring in little corners in the groundmass which resembles 

 the melilite, but seems to have a much lower index of refrac- 

 tion and. never shows "peg structure." This is probably a 

 little nepheline, but after carefully studying a large number of 

 thin sections no positive proof on this point could be obtained 

 as the mineral has not a good crystalline form. The other 

 constituents of the rock exhibit no peculiarities deserving of 

 further mention. 



The order of crystallization of the principal constituents is 

 as follows : First, the magnetite, then olivine, biotite and 

 pyroxene of the first generation in the order named, then 

 probably another generation of olivine, followed certainly by a 

 second generation of pyroxene and biotite while the melilite 

 has crystallized last of all. 



The secondary minerals filling the cavities before mentioned 

 are quartz and calcite. The former mineral is represented for 

 the most part by microcrystalline and cryptocrystalline vari- 

 eties. The calcite occasionally shows excellent pleochroism, 

 yellow and colorless. A little opal and a small quantity of 

 some zeolite are probably also present in a few cases. These 

 are not primary but true secondary cavities eaten out of the 

 various constituents of the rock. 



