78 



PROCEEDINGS OF THE NATIONAL MUSEUM. 



VOL. 66. 



The apopliyllite of the analyzed sample is biaxial positive ( +) with 

 2V very small, r< v strong, a=-^= 1.534, 7= 1.537. 



In addition to the platy forms apophyllite also occurs as distinct 

 crystals. The simplest of these are tetragonal square prisms termi- 

 nated by a basal pinacoid, greatly resembling cubes. Some crystals 

 of this type reach 3 cm. in diameter. The largest crystals are dull 

 externally and their outer layer has a pinkish color, although the inte- 

 riors are transparent and colorless. One specimen shows a narrow 

 vein 1.5 cm. wide with tufts of laumontite crystals grown from either 

 wall and the central portion filled with cleavable apophyllite. Small 

 cavities in this vein contain cubical crystals of apophyllite up to 8 mm. 

 on an edge. The prismatic faces are horizontally striated and the base 

 has a pearly luster. Such crystals are illustrated in figure 27. Some 

 of these are partly coated with minute colorless scalenohedral crystals 

 of calcite. 



Many of the smaller apophyllite crystals which are interspersed with 

 or rest upon stilbite crystals are acute pyramidal with the simple habit 

 shown in figure 28, or the slightly more modified habit of Figure 29. 

 Such of the crystals of this type as were measured gave the following 

 average angles: 



Measurements of apophyllite crystal, Figure 28. 



Form. 



No. Letter, 



a 



m 



y 



New 

 V 



Symbol. 



Gdt. 



Ooo 



CO 



co3 



oof 



1 



Miller. 



Quality de- 

 scription. 



010 

 110 

 130 

 350 

 111 



Measured. 



Calculated. 



Fair 00 90 00 00 



Very poor — very narrow — no signal. 



Fair I 18 29 



Poor 29 46 



Very good 1 45 15 



90 00 i 18 26 

 90 00 30 58 

 60 18 45 00 



90 00 



90 

 90 

 60 



00 

 00 

 32 



The triangular markings on the prisms (130) and (350) are a pecu- 

 liar feature of the crystals as shown in figure 29. The prism (350) is 

 apparently new but it is not definitely established by these measure- 

 ments. There is a rounding of the faces of these two prismatic forms 

 and neither gives satisfactory signals. 



Translucent small white crystals resting on a crust of prelmite col- 

 lected by Drs. Merrill and Wherry have the habit shown in figure 30. 

 These gave the following angles : 



