THE MINERALS OF IDAHO 



357 



7?2 



LAUMONTITE (445) 



Hydrous lime-alumina silicate, Monoclinic. 



CaO.Al203.4Si0 2 .4H 2 0. 



Laumontite is a member of the zeolite group, which is peculiar in 

 that it looses a part of its water of crystallization upon exposure to 

 air and usually turns white and disintegrates. Small amounts of this 

 mineral have been found in Idaho in Blaine and 

 Kootenai Counties. 



BLAINE COUNTY 



Specimens of laumonite were collected by D. F. 

 Hewett of the United States Geological Survey in 

 the Wood River district, especially at the Bellevue 

 King prospect near Bellevue. The laumontite, 

 which is typical in appearance, lines seams in a 

 chloritized rock, and also occurs as veinlets up to 2 

 cm. thick, which are filled in the center with calcite. 

 The crystals, which are rarely over 2 mm. in 

 length, are prismatic with the common habit illus- 

 trated in Figure 118. 



KOOTENAI COUNTY 



A few prismatic imperfect crystals of laumontite 

 occur with stilbite, prehnite, etc., coating a fracture 

 in diabasic rock in a specimen from Post Falls in 

 Kootenai County. 



CHABAZITE (447) 



Variable hydrous silicate of lime, alkalies Rhombohedral. 



and alumina approximating the formu- 

 la (Ca,Na 2 ,K 2 )O.Al 2 3 .4Si02.6H 2 0. 



Three occurrences of zeolites which have been 

 referred to chabazite have been examined. One of 

 these is in a contact-metamorphic deposit in lime- 

 stone and two are in cavities in lavas. The two 

 latter have only been included under this species 

 after much consideration and may, upon more de- 

 tailed investigation than was permitted by the scanty material avail- 

 able, be found to be in reality some other member of the zeolite 

 group. 



ADAMS COUNTY 



A specimen from the Blue Jacket claim in the Seven Devils district 

 contains chabazite, with less stilbite and heulandite, deposited on 

 crack and joint surfaces in massive brown garnet rock. The chaba- 

 zite is the most abundant of the three zeolites of the specimen, and 

 forms simple rhombohedral crystals, illustrated in Figure 119, of an 



Fig. 118.— Laumon- 

 tite. Common 

 habit. Belle- 

 vue Kino pros- 

 pect near Belle- 

 vue, Blaine 

 County 



