112 8. L. Penfield — Analcite from Phoenix Mine. 



Art. XV. — Crystals of Analcite from the Phoenix Mine, LaJae 

 Superior Copper Region ; by Samuel L. Penfield. 



These crystals which have lately been received at New Haven, 

 occur thickly grouped together on calcite and native copper, 

 associated with tabular crystals of apophyllite, and numerous 

 minute crystals of milky quartz scattered thickly over the speci- 

 mens. The crystals are of all sizes from very minute up to one 

 centimeter in diameter; the small ones are simply tetragonal- 

 trisoctahedrons of the form (211), 2-2, the larger ones are of the 

 same form but with the planes arranged as in fig. 1. Along 

 every edge of what might be regarded as a simple crystal, there 

 is a reentrant angle or groove. The crystals are mostly of ideal 

 symmetry of arrangement, and appear as if made up of twenty- 

 four simple crystals, each equally spaced from the center. 

 Occasionally at the extremity of the principal axes, a fifth solid 

 angle can be seen symmetrically situated midway between the 

 four represented in the figure. The planes of the crystals are 

 uneven, as is so often the case with analcite, so that it was im- 

 possible to prove by means of the reflection goniometer that the 

 individual parts of the crystal were arranged in exactly parallel 

 position. 



In order to obtain some insight into the interior arrangement 

 of the crystals, some sections were cut and examined with the 

 microscope. A cross section parallel to (001), i-i, at the point 

 a, fig. 1, is given in fig. 2. The section is plainly divided into 

 four parts corresponding to the four crystals, so to speak, which 

 are intersected at that point, the division lines running nearly 

 parallel to the diagonals of the rectangle. The figure shows the 

 irregular direction of these dividing lines in one of the sections, 

 at times they run much more regularly. They were observed 

 in all cases, and can be seen with the naked eye as soon as 

 the top of the crystal is cut away. After grinding the sections 

 thin it is impossible to transfer the same to an object-glass with- 

 out the four parts separating along these division lines, and this 



