L. V. Pirsson — Mordenite. 233 



terial obtained in that region, this specimen came to light and 

 as some tests failed to classify it, a complete investigation was 

 undertaken with the results here presented. In order to obtain 

 enough material for analysis nearly the whole of the specimen 

 had to be sacrificed. As the mordenite occurs in very small 

 crystals, one of average size measuring under the microscope 

 1™ in height and breadth by about *4: mm in thickness, it would 

 have been impossible to pick out sufficient pure material for 

 analysis. 



A preliminary specific gravity determination showed it to 

 be about 2*14 and it was therefore determined to separate it 

 by means of the Thoulet solution, it being so much lighter 

 than the pyroxene and other minerals that might be expected 

 in the basalt. The specimen was therefore crushed fine enough 

 to pass through an 80 mesh sieve, washed free from dust and 

 twice separated by the Thoulet solution. In the last operation 

 the mordenite floated on a solution of 2 -179, and sank when 

 the density was lowered to 2*119. Its specific gravity is there- 

 fore between these two determinations. The density of the 

 Thoulet solution was taken with a Westphal balance. 



The material thus obtained after washing and drying, proved 

 on examination under the microscope, to be of exceptional 

 purity, consisting wholly of crystal fragments, showing charac- 

 teristic outlines and cleavage, and with no adherent particles 

 of any foreign substance. The greater part were perfectly 

 transparent and colorless, occasional fragments showed a very 

 pale brownish discoloration in spots, as if due to the infiltra- 

 tion and deposition of a minute amount of iron ore or organic 

 matter into cleavage cracks. In no respect as to appearance or 

 their action on polarized light did these latter differ from the 

 colorless pieces. 



A test was again made with the Thoulet solution to ascer- 

 tain if any difference in specific gravity could be found 

 between the two. Very careful testing failed to show any 

 whatever. Both floated and sank at precisely the same densi- 

 ties and in precisely the same proportion. Great confidence is 

 therefore felt in the' purity of the material operated upon. 

 The perfect separation by the Thoulet solution was no doubt 

 due to the heavy, crumbly nature of the basalt with which the 

 mordenite was associated and its own brittleness and low spe- 

 cific gravity. By this means about one gram of the pure min- 

 eral was obtained. It was thoroughly washed and dried at 

 about 70° F. It was then finely powdered and subjected to 

 analysis. A preliminary test showed that the mineral was 

 scarcely attacked by boiling hydrochloric acid. The material 

 was therefore divided into two equal portions and in the first, 

 which was brought into solution by a mixture of sulphuric and 



