the apex, and 2-1/2 inches
wide at the base. Most of the crystal is a deep grass green, but at the
base the outer green layers have shelled off, revealing a cone of deep
pink, which, however, does not appear to penetrate far. The base, a
nearly straight surface inclined about 70° to the main prism axis,
appears to be a fracture surface and is conchoidal. It is partly coated
with cookeite, as are the lower flanks of the prism, showing that the
crystal had become detached from its original position on the wall of
the pocket before the cookeite was deposited. The summit terminations
are not crystal faces, but are fracture planes standing nearly at right
angles to the main axis. The sides are closely and beautifully
striated. The crystal is transparent to translucent and does not
appear to contain any gem material. This tourmaline was the largest
found in the giant pocket shown in Plate XIII. It lay loose in the
bottom in a mass of kaolin and of cookeite sand. A few other smaller
tourmalines were found, but none were of gem quality, and in proportion
to its great size the pocket was remarkably unproductive. The pocket
contained large amounts of massive and crystal quartz plugged full of
small opaque tourmaline crystals. In one end there was about a ton of
the pink kaolin montmorillonite.
The
largest transparent crystal of green tourmaline found at Mount Mica was
discovered by Samuel R. Carter in 1886 and is now in the Cambridge
Museum of Natural History. It is 10 inches in length, 2-1/4 inches in
diameter, and weighs 41 ounces. Both terminations have been preserved,
but they are not at all perfect." Although broken into four pieces, the
parts have been easily joined by cement. Its middle portion would
probably yield some fine gems. This crystal came from an unusually
large pocket 4 feet in diameter, along whose sides and at whose bottom,
embedded in a sand of decomposed cookeite, lepidolite, etc., were
found fragments of certainly 50 well-defined tourmaline crystals.
The
most remarkable crystal of white tourmaline or achroite found at this
locality is also in the Cambridge Museum of Natural History. It was
obtained in 1869 from a large pocket which yielded several other
crystals of smaller size. This crystal is transparent, but when viewed
in light transmitted at right angles to its axis appears smoky toward
the base; when viewed along the axis its hue is crimson. Both ends are
tipped with green, but its terminal faces are not preserved. Its length
is about 4 inches and its width 1-1/2 inches.
The
finest crystal of blue tourmaline or indicolite found at Mount Mica is
in the Hamlin cabinet. It is transparent throughout its entire shaft,
although broken into five parts. Both terminations are preserved. The
color, when viewed at right angles to the prism
