. Bulletin - United States National Museum. Science. 358 BULLETIN 131, UNITED STATES NATIONAL MUSEUM amber-brown color averaging 2 mm. on an edge. Under the micro- scope the powdered chabazite shows very low birefringence. Differ- ent grains from the same crystal give both positive and negative biaxial interference figures, with 2V medium large to small. The mean refractive index varies from to BOISE COUNTY Specimens labeled as from Warm Springs Creek east of Boise, con- sist of very vesicular basaltic rock, containing abundant cavities up to 2 cm. in diameter largely filled with
. Bulletin - United States National Museum. Science. 358 BULLETIN 131, UNITED STATES NATIONAL MUSEUM amber-brown color averaging 2 mm. on an edge. Under the micro- scope the powdered chabazite shows very low birefringence. Differ- ent grains from the same crystal give both positive and negative biaxial interference figures, with 2V medium large to small. The mean refractive index varies from to BOISE COUNTY Specimens labeled as from Warm Springs Creek east of Boise, con- sist of very vesicular basaltic rock, containing abundant cavities up to 2 cm. in diameter largely filled with a white zeolite which is referred to chabazite. The rock is a basalt, and contains conspicuous grains of iddingsite, the properties of which are given under that heading. The locality is given as on Warm Springs Creek, which is a tributary to Payette River from the north near the center of the Bear Valley topo- graphic map area. The zeolite forms crusts of intergrown color- less to whitish transparent to translucent crys- tals nearly filling many of the cavities. The crystals are not well developed and are grouped in complex twinned aggregates. When the Fig. 119.—Chabazite. Simple „ ., ,, , „ , - , unit rhombohedron. forms are at all well denned they have a seven devils district, rhombohedral appearance, but no good meas- Adams County ... , . G ,. ,. urements could be obtained. Some white radi- ated thomsonite is associated with the chabazite, and in many of the cavities there is a clayey greenish material between the chabazite and the wall of the vesicule. Optical determinations gave varied results on material which, under a binocular microscope, appeared to all be the same. Accord- ingly a quantity of the material was crushed and screened and treated with heavy liquids by which process a light, an intermediate, and a heavy product were obtained. The light product appeared homogeneous under the microscope and was transparent and colorless with uniformly low birefringence
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