occurring near Pike's Peak, Colorado. 285 



boundary between the two masses of quartz is sharply drawn, 

 but the development of the tunnel is not extensive enough to 

 show clearly the relation of the two bodies. 



Throughout the greater part of the vein the zircon is 

 imbedded directly in the quartz and is so abundant that a 

 cubic inch of the latter mineral contains from 25 to 100 crys- 

 tals and particles of zircon, varying in size from l cm downward. 

 Id parts of the vein, however, are small, irregular spaces filled 

 with a soft, yellow foliate mineral in which are imbedded very 

 perfect crystals of zircon. Fluorite and a white foliate mineral 

 are sometimes associated with the others. The two foliate 

 minerals are as yet undetermined. 



This occurrence is worthy of special notice on account of 

 the perfection of the crystals and their transparency. Some of 

 the crystals lying in the quartz are perfectly developed, but 

 usually their growth has been more or less hemmed by the 

 quartz, and many are fissured. The crystals imbedded in the 

 soft, yellow material, however, are often absolutely perfect in 

 form, and beautifully clear. The ruling color is a deep red- 

 dish-brown with variations toward pink or a pale honey-yellow. 

 A few crystals are of a deep emerald-green, and spots of the 

 same were noticed in some of the pink crystals. 



The common habitus of all crystals is pyramidal, the prisms 

 being alwavs subordinate when thev appear. The forms 

 determined with certaintv are. 1 (/>), 3'(3P), O(0P), 3S (3P3), 

 /(»/>) and i-i (oo Poo). The rare face is much less fre- 

 quently developed than any of the others but it was observed 

 distinctly on at least twenty-five crystals. Repeated measure- 

 ments on different crystals of the angle 6>Al give results vary- 

 ing less than 3' from the calculated value (137° 50'). Between 

 and 1 is a low pyramid appearing quite constantly with O, 

 which forms an angle of 16*4° 46' with 1. This corresponds 

 very nearly to l|(^|P). The angle between this form and 1 

 is a curved surface "giving an almost continuous reflection, but 

 the angle with O is distinct. The crystals showing occur in 

 the soft, yellow substance, and the face in question could not 

 have been formed by pressure of the surrounding material. 

 The face was noticed by Konig (1. c.) on the zircon occurring 

 with astrophvllite, but his statement has been either overlooked 

 or discredited, as Zirkel, in the recent edition of Naumann's 

 "Elemente der Mineralogie," says that has not yet been 

 observed, though he cites an analysis by Konig of the same 

 zircon which showed the basis 0. On all but one of our crys- 

 tals and the pyramid || are developed on one end only, the 

 other showing simply 1, thus giving a hemimorphic appear- 

 ance to the crystal. 



The chemical investigation of this zircon shows it to be 



