Weidman and Lenher — Marignacite. 289 



The mineral has a hardness of 5 to 5*5, a specific gravity of 

 4*13. The cleavage is indistinct, the mineral is brittle and 

 breaks with a conchoidal fracture. The lustre is resinous on 

 fractured surfaces. The streak is light brown to yellowish 

 brown. The color varies from a light to dark brown in the 

 hand specimen, while under the microscope a yellow brown to 

 red brown is shown. 



It is sub-translucent to transparent. The index of refraction 

 is relatively high and anomalous double refraction is character- 

 istic. Before the blowpipe it is infusible and unchanged. In 

 the borax or salt of phosphorous bead, it dissolves with a yel- 



low color while hot, and is colorless when cold. The mineral 

 is very refractory to the acids, and is only slightly attacked 

 by fused sodium carbonate. It is attacked in the cold by 

 hydrofluoric acid, and can be decomposed by fusion with either 

 potassium acid sulphate or potassium acid fluoride. 



For analysis the mineral can be decomposed either by fusion 

 with potassium acid sulphate, in which case the silica and 

 metallic acids can be separated from the earths, etc., or it can 

 be decomposed by treatment with hydrofluoric acid, when the 

 metallic acids pass into solution, leaving the earthy fluorides 

 insoluble. 



Silica was estimated in the residue obtained from repeated 

 extractions of a bisulphate fusion by volatilization with hydro- 

 fluoric acid in the presence of sulphuric acid. The columbic 

 and tantalic acids were tested for tin, molybdenum, tungsten, 

 titanium and the earths. The titanium was separated from 

 them by a bisulphate fusion, and the metallic acids were sepa- 

 rated by the Marignac method of crystallizing the double 

 potassium fluorides from each other. It is perfectly well 

 appreciated that the results for columbium and titanium are 



