36 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 71 



The stilbite is often associated with the grossular garnet or occurs 

 in the cavities in the hornfels with vesuvianite and chabazite. In 

 those specimens which contain the vesuvianite the stilbite often forms 

 a single rosette of radiating blades in the cavity in garnet-diopside 

 or garnet hornfels. Often associated with the rosette are a few 

 crystals 2 mm. or less long of the common stilbite habit. One speci- 

 men contains scattered compound white pearly stilbite crystals up to 

 3 by 5 mm. in size projecting through and older than a crust of 

 chabazite. The stilbite overlies some scolecite or rests upon vesuvia- 

 nite in a cavity in hornfels. (No. 84545.) 



Specimens of loosely aggregated masses of amber crystals of 

 grossular garnet have all the interstices lined with drusy crusts of 

 minute colorless crystals of stilbite of the usual habit. A similar 

 mass of large brown garnets has thin drusy crysts made up of very 

 minute sharp and colorless crystals of epidesmine habit, with heulan- 

 dite, resting on garnet crystals or on albite which occurs in small 

 amount. The grains of stilbite, under the microscope, lie on a per- 

 fect cleavage, which is parallel to the optic plane and show rectangu- 

 lar outline. The indices are «= 1.486, y= 1.498. The optic orienta- 

 tion, assuming the best cleavage to be (010) and the long direction 

 vertical is Z=(7, Y=Z>, X A c = 3°. In one case stilbite on garnet 

 crystals is overlain by later chabazite and calcite. (No. 84551.) In 

 one specimen small colorless stilbite crystals resting on a mass of the 

 light colored grossular garnet are partly overlain by a thin coating 

 of pinkish clay. The larger of the stilbites, which reach only 2 mm. 

 in length, show normal habit. — a rectangular prism determined by the 

 front and side pinacoids with pearly luster on the broad face (010), 

 surmounted by a basal pinacoid and with four truncating pyramid 

 faces, the whole modified somewhat by the aggregate character with 

 slight divergence. The smaller crystals of this specimen have a very 

 unusual triclinic appearance. They are flat prismatic by elongation 

 of the faces (100) and (010), truncated at the summit by a single 

 oblique face, probably one face of the unit pyramid, developed to the 

 exclusion of the other terminal faces. 



In a few specimens the stilbite is the most conspicuous mineral. 

 Its age relation to the other zeolites is not always clear. One speci- 

 men (No. 84575) shows a few obscure rosettes of blades of stilbite 

 up to mm. in diameter, partly underlying a drusy crust of 

 heulandite encrusting a dense whitish hornfels. This specimen is 

 labeled heulandite from the Bidwell Range. Another specimen 

 labeled as from Taylor Peak, Italian Mountain, consists largely of 

 pale buff stilbite in small rosettes of radiating blades. This, when 

 crushed and examined under the microscope, shows elongate frag- 

 ments which lie on a good cleavage perpendicular to the optic nor- 



