252 THE CliYSTAL FALLS IRON-BEARING DISTRICT. 



included biotite or olivine, these two minerals have associated with them 

 numerous small grains of ore, which probably represent the iron that 

 would have been incorporated in the surrounding hornblende but for some 

 selective influence exerted by the olivine and biotite. 



Biotite. — This mineral is present in flakes of very irregular outline. The 

 pleochroism varies from cream color to yellowish red or brown. Although 

 one of the last minerals to crystallize, its crystallization began before that of 

 the pj^roxene or hornblende had entirely finished. Hence we find flakes of it 

 included in these minerals, but near the edges of the crystals. The biotite 

 itself is almost free from inclusions, containing only a little hematite and mag- 

 netite. It alters to a brilliant green, strongly pleochroic, chloritic mineral. 



Feldspar. — This is prcscnt in specimens from two outcrops, and in these 

 hardly reaches the rank of an essential constituent. It was the last mineral 

 to crystallize, and is consequently in anhedra, forming the mesostasis. All 

 of the feldspar sections were tested, but no determinative measurements 

 could be made. It is probably very basic. 



Apatite. — Apatite is present in small quantity. It exhibits its usual 

 characters. 



Spinel. — There is a spinel found in round grains which are included in 

 the olivine (serpentine). It is green in color, and is possibly pleonaste. A 

 second spinel, probably picotite, occurs in small brown grains and octahedra 

 in the olivine. 



caicite. — This mineral, derived partly, if not wholly, from the altering 

 minerals, is found in lenses between the biotite lamellse and in minute veins 

 which traverse the slide. 



Iron ores. — Irou Ore is represented by hematite, magnetite, and pyrite. 

 The hematite is in blood-red transparent flakes inclosed in the biotite. 

 Magnetite is included by all of the chief minerals, and is in irregular masses 

 without good crystal development. The iron pyrite is found in good crys- 

 tals, though not in large quantity, and is scattered here and there through 

 the slides. 



PERIDOTITE VARIETIES. 



The relative proportions of the minerals described above differ very 

 much, and we have different kinds of rocks corresponding to these min- 

 eralogical variations. These kinds are not sharply separated, but are seen 

 under the microscope to grade into one another. 



