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 ervstal
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 microscope by their high refractive index,
negative elongation with maximum angle of extinction 2° or 3° ;
pleochroism, ο deep grass green, h lighter green, t brown to yellow; absorption The needles melt readily before the blowpipe, with a strong sodium flame, to a black magnetic globule.
Calcite and Aragonite.
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
stringers and coatings of manganese dioxides are common 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
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.