Vol. 5] Louderback.—Benitoite. 363 



p(Tll) on lower side of twin was determined as being in zones 

 TTl -131-010, and 001-1T0. 



The extinction on cleavage flakes parallel to (010) is — |— 18 ° ; 

 on (001) +4? + . 



Aegyrine. 



At one point there was found in the albite a belt several inches 

 long - of stellate groups referred to aegyrine. The color is greenish 

 black. The individuals, sometimes as much as 6 or 8 mm. long, do 

 not show crystal form and are exceedingly thin in one dimension, 

 corresponding to the tendency of aegyrine to form needles very 

 flat parallel to (100). They were determined under the micro- 

 scope by their high refractive index, negative elongation with 

 maximum angle of extinction 2° or 3° ; pleochroism, o deep grass 

 green, 6 lighter green, c brown to yellow ; absorption a > 6 > c. 

 The needles melt readily before the blowpipe, with a strong 

 sodium flame, to a black magnetic globule. 



Calcite and Aragonite. 



Crystallized calcium carbonate has not been observed in the 

 benitoite-natrolite veins, but is not uncommon in the adjoining 

 rocks, especially in the altered basic rocks on the south side. It 

 occurs as stringers and bunches. While calcite is the more 

 common form, specimens of aragonite were obtained in radiate 

 groups of columns 1 to 4 mm. thick. They are translucent and 

 have a slightly brownish tint and while not showing terminal 

 planes, the prismatic and pinacoidal cleavages are well developed. 

 They carry on their surfaces small, white, more opaque calcite 

 rhombohedra. 



Manganese dioxide. 



Thin stringers and coatings of manganese dioxides are com- 

 mon in the country on the north side just below the cut. It, 

 generally shows the character of psilomelane and is frequently in 

 fine globular and botryoidal aggregates. 



While it may sometimes be found in the same hand-specimen 

 that carries the benitoite veins, it does not actually occur in these 

 veins in which the manganese is limited to the neptunite. 



