208 S. L. Penfield — Choi copy rite from Chester Co., Pa. 



fine fibrous mineral is insoluble in acids, fuses like hornblende 

 and is probably a variety of that mineral called byssolite ; the 

 compact scaly mineral is soluble in hydrochloric acid, fuses 

 B. B. at about 3 to a black magnetic globule, contains only 

 traces of magnesia, gives abundant water in the closed tube 

 and is probably thuringite. The byssolite and thuringite 

 fill cavities or pockets in the magnetic iron ore and are at 

 times thickly beset with crystals of both chalcopyrite and 

 pyrite, while again large quantities of the material may be 

 examined without finding any. Most of the chalcopyrite crys- 

 tals have the characteristic brass-yellow color, while some show 

 a purple tarnish, and others are coated with a black oxide. 

 The crystal faces are always striated parallel to their intersec- 

 tion with the positive and negative unit sphenoids, frequently 

 causing a rounding or distortion of the crystals and entirely 

 unfitting them for exact measurement on the goniometer. 



The simplest type of crystal is the sphenoid r, 332, § fig. 1. 

 The angle of rs\.r, 332 /\ 332 measured approximately 130°, cal- 

 chlated from c = 0*9856, 128° 52'. This same sphenoid r is at 

 times found with its solid angles modified by the faces of a 

 tetragonal scalenohedron a>, fig 2. By placing the arms of a 

 contact goniometer along the longer pole edges of the scaleno- 



hedron it was found that they made an angle of about 155°, 

 from which it was calculated that the sphenoid 116,-A, would 

 truncate the edges, while the vertical striations on the faces 

 indicated their probable oscillation with the unit sphenoid, 111. 

 By a combination of zones it was found that 576, |— f, 

 would satisfy these conditions, and although it is not at all cer- 

 tain that this is the true symbol, fig. 2 gives one a fair idea of 

 the habit of the crystals. 



A very common type is represented in fig. 3. The sphenoid 

 <p varies much in inclination in different crystals, in some it is 

 nearly vertical like a prism, in others inclined almost as much 

 as the | sphenoid r. It is not at all certain, therefore, 

 whether it is a prism, which tapers owing to oscillations with 



