An Expedition to Mount St. Elias, AlaskaRussell, Israel C. (Cook)
History
An Expedition to Mount St. Elias, Alaska
Russell, Israel C. (Cook)
Alaska -- Description and travel; Saint Elias, Mount (Alaska and Yukon)
Two species were noted: one is a brilliant wine-red variety, which,
though not nearly so numerous as its duller relative, occurs more
frequently in crystals--the trapezohedral faces (211, 2-2)
predominating. The other garnet is readily distinguished by its
lighter amethystine tint and its greater abundance. Crystallographic
faces are somewhat rare and invariably dodecahedral (110, i). In the
absence of chemical analyses, any statements as to the exact species
to which these garnets should be referred would be largely
conjectural. Attention is quickly drawn to the perfection of these
minute garnets in their crystallographic faces and outlines, and to
their association with rounded fragments of their own kind as well as
of other minerals. Have these crystals survived by reason of their
hardness or by favoring conditions, or does their preservation suggest
the impotency of wave-action in the destruction of minute bodies?
Among the black, heavy grains occur individuals which, except in shape
and non-magnetic character, resemble magnetite. On crushing between
glass slides, thin slivers are obtained which in transmitted light are
green, and which, from their cleavage, pleochroism, high index of
refraction, small extinction angle, and insolubility in acid, are
readily recognized as hornblende.
Two groups of grains were noted which are distinguishable by slight
variation in color. Both are clear-yellowish green, but one is
somewhat darker than the other. The optical properties of both
indicate pyroxene and possibly olivine. Fortunately a fragment was
obtained in the orthodiagonal zone nearly normal to an optic axis
which gave an axial figure of sufficient definiteness to indicate its
optically positive character. A number of grains were selected from
minerals of both colors and subjected to prolonged heating in
hydrochloric acid without decomposition, indicating that both minerals
are pyroxene.
A few zircons, a fraction of a millimeter in size but perfect in form,
were found associated with others rounded on their solid angles and
edges. The crystals are of the common short form and bear the usual
faces in a greater or less degree of development. Pyramids of the
first and second order alternate in magnitude; pinacoid encroaches
upon prism, and _vice versa_.
Quartz constitutes by far the largest proportion of the minerals, both
in bulk and in weight. It is always fragmental; sometimes water-clear,
but chiefly occurs in opaque grains of different colors. It is seldom
free from material of a higher specific gravity, and is often so
tinted as to be almost indistinguishable from magnetite, but readily
bleaches in acid.
{198} Feldspar is sparingly present, and includes both monoclinic and
triclinic forms, whose crystallographic boundaries are invariably
lacking.
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