ART. 18 MINERALS OF ITALIAN" MOUNTAIN CROSS AND SHANNON 31 



to a greater or less degree by a fine fibrous mineral which has devel- 

 oped parallel to the vertical axis. This mineral has negative elonga- 

 tion and an index of refraction of about 1.515 and is probably scole- 

 cite. Scattered clear grains which also occur in the powder are 

 colorless and isotropic or with very feeble birefringence and an index 

 of 1.485. This mineral is probably analcite. In a few cavities in 

 these specimens considerable areas are covered with drusy termina- 

 tions of perfect little heulandite crystals. 



The second large lot of scapolite specimens (No. 84568—9 speci- 

 mens) is labeled " scapolite in diorite, south slope of Sawtooth Range, 

 Taylor R. Gunnison County." These contain veins of solid grayish- 

 white compact scapolite up to 6 cm. wide with borders % cm. wide 

 on each side of a mixture of scapolite and a green mineral, probably 

 diopside. These cut fine grained diorite. The scapolite shows 

 cleavage blades up to 1 by 6 cm. Under the microscope this scapo- 

 lite is comparatively fresh and free from alteration. It is uniaxial 

 negative ( — ). The refractive indices are, £=1.542, (orr:1.558, bire- 

 fringence, w — err:. 016. 



The third group of specimens (84566), labeled "scapolite with 

 byssolite, Italian Mountain," consist of loose textured masses of 

 rude dirty white prisms up to 1 by 3 cm. forming a network, the 

 interstices of which are filled with byssolitic hornblende. These 

 prismoidal masses are to a large extent corroded and replaced by a 

 dull fine-fibrous zeolite which has the properties of scolecite. Where 

 they contain cores of unaltered material this is uniaxial negative with 

 negative elongation; indices, e= 1.542, w= 1.550. The scolecite and 

 byssolite. as Avell as the heulandite and titanite which occur in the 

 cavities, are described elsewhere. 



A single specimen (No. 84567) is largely composed of radiating 

 fine columnar bundles of prismatic scapolite, white in color and 

 slightly pearly in luster. The bundles average 1 cm. broad by 4 cm. 

 in length. In vuggy parts of the specimen the scapolite forms rude 

 crystals up to 3 by 15 mm. Pyrite, altered to lustrous limonite 

 pseudomorphs, occurs in thickly scattered crystals up to 5 mm. in 

 diameter, resting on the scapolite. Optically this scapolite is uni- 

 axial negative with refractive indices of approximately e=1.539, 

 t(7=1.549, which indices indicate that it is mizzonite. Some altera- 

 tion to scolecite gives parts of the scapolite lower indices and 

 birefringence and a fibrous structure. 



Another single specimen (No. 84567) shows rude white prismatic 

 masses up to 8 by 20 m.m. coating the face of a sheeted rock which is 

 itself largely scapolite. This material has the refractive indices 

 cj=1.553, £=1.541. 



