130 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
tourmaline in luxullianite or as single prismatic crystals contained 
in the feldspar, lying either parallel to the c axis or obliquely to the 
twinning plane. A drawing of a particularly characteristic group of 
these crystals is shown below taken from slide 25,609 of the series 
prepared for the Tenth Census and kindly 
loaned by the U. S. National Museum through 
Prof. Geo. P. Merrill. Professor Merrill writes, 
“the beautiful blue acicular crystals (sec. 
25,616) were never determined by me, and I 
find no certain reference to them in Hawes’s 
notes, although on section 25,609 he had writ¬ 
ten in pencil ‘ Draw,' as though he had worked 
it out mentally but not committed himself in 
writing.” 
The needles show the greatest absorption 
very nearly parallel to the longitudinal axis. 
More rarely they give an appearance of 
absorption at right angles, so as to be easily mistaken for tourmaline, 
which the form and occurrence strongly suggest. The edges of 
the larger needles are often blue, seemingly indicating a soda amphi- 
bole, at least as a growth surrounding the original needles. They 
show high refraction; and as the arrangement of the needles in the 
fluidal rhyolites, in which they also occur, agrees with the fluxional 
arrangement, they evidently crystallized in an early stage of the 
magma. Separate needles when inclosed in the plagioclase form an 
angle of about 19° with the striations of the inclosing feldspar. 
The writer at first thought these crystals to be riebeckite, a soda 
amphibole intermediate between aegirine and pyroxene; which latter 
as Rosenbusch says (’92, Yol. 1 p. 566) it strikingly resembles. Rie¬ 
beckite occurs in a similar manner in the granite of the island of 
Socotra (Sauer,'’88). Bonney (’73, p. 283) at Socotra mistook the 
mineral for tourmaline pseudomorph after hornblende, but Sauer 
thinks it is at least in part, an alteration of the feldspar. Harker 
(’88) describes black to bluish crystals agreeing very nearly with 
these as a blue hornblende, from granites and felsites at Mynydd 
Mawr, near Snowdon, Wales, which he afterwards identified as 
riebeckite. 
Careful determinations with the gypsum plate, on a number of 
sections of the Quine} 7 mineral, in order to determine the position of 
its axes of elasticity, seem to indicate an optically positive mineral. 
The test is rendered difficult by the minute size of most of the 
