" Fibrous rocks are
comparatively rare, in mass; but fibrous minerals are innumerable;
and it is often a question which really no one but a young lady
could possibly settle, whether one should call the fibers
composing them "threads" or "needles." Here is amianthus, for
instance, which is quite as fine and soft as any cotton thread you
ever sewed with; and here is sulphide of bismuth, with sharper
points and brighter luster than your finest needles have; and
fastened in white webs of quartz more delicate than your finest
lace; and here is sulphide of antimony, which looks like mere
purple wool, but it is all of purple needle crystals; and here is
red oxide of copper (you must not breathe on it as you look, or
you may blow some of the films of it off the stone), which is
simply a woven tissue of scarlet silk. However, these finer
thread-forms are comparatively rare, while the bolder and needle-
like crystals occur constantly; so that, I believe, "Needle-
crystal" is the best word (the grand one is, "Acicular crystal,"
but Sibyl will tell you it is all the same, only less easily
understood; and therefore more scientific). Then the Leaf-
crystals, as I said, form an immense mass of foliated rocks; and
the Granular crystals, which are of many kinds, form essentially
granular, or granitic and porphyritic rocks; and it is always a
point of more interest to me (and I think will ultimately be to
you), to consider the causes which force a given mineral to take
any one of these three general forms, than what the peculiar
geometrical limitations are, belonging to its own crystals.
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