38 PROCEEDINGS OF THE NATIONAL MUSEUM vol.71 



number consists of a crust of heulandite coating a crack in reddish 

 sandstone. The heulandite overlies a druse of small prismatic quartz 

 crystals. 



Minute heulandite crystals of " beaumontite " habit make up small 

 drusy bristling masses overlying small greenish-buff crystals of 

 grossular garnet. (No. 84553.) Other crystals too minute for their 

 form to be made out make up radiating masses or drusy crusts on 

 scattered albite in the interstices of a mass of large brown garnets. 

 Optically these are biaxial positive with the acute bisectrix perpen- 

 dicular to the most perfect cleavage. The axial angle approximates 

 50 to 60° and the crystals are zoned in refractive index the indices 

 being approximately a = 1.486—1.490, (3 = 1.492, y r= 1.498. 



A large specimen of mizzonite has a cavity on one side lined over 

 a considerable area by a drusy crust made up of perfect termina- 

 tions of minute colorless heulandite crystals (No. 84567). Specimens 

 composed principally of mizzonite, scolecite, and byssolite (No. 

 84566) contain small hexagonal-appearing crystals embedded in the 

 byssolite. These reach 3-4 mm. in diameter, are pearly lustered on 

 the broad face and are colored greenish by included fibers of bys- 

 solite. Under the microscope their material is colorless, shows low 

 birefringence and rests upon a perfect cleavage which is perpen- 

 dicular to the acute bisectrix. The mineral is optically positive with 

 2V very small, dispersion r < v perceptible, y3= 1.500. This mineral 

 is doubtless heulandite. 



CHABAZITE 



Chabazite occurs most commonly in the cavities in the vesuvianite 

 specimens where it overlies vesuvianite crystals and is almost an 

 invariable associate of this mineral. It forms white crystals, mostly 

 simple rhombohedrons with a few penetration twins which vary from 

 1 to 5 millimeters or more on an edge. Many of these are almost 

 model-perfect. While chabazite is the most abundant zeolite in these 

 cavities it is often associated with small amounts of stilbite and 

 scolecite, both of which seem to be older than the chabazite. 



In one specimen a few small rhombohedral crystals are associated 

 with scattered quartz and titanite crystals overlying a druse of albite. 



Another specimen (84572) from the south slope of the Sawtooth 

 "Range has colorless to white simple rhombohedral crystals of chaba- 

 zite up to 2 millimeters in diameter coating one broad surface of a 

 mass of unaltered diorite. 



Under the microscope the material associated with the vesuvianite 

 shows very low birefringence and a refractive index of about 

 1.482-1.484. 



