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MANHATTAN ISLAND 145
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This mineral was very commonly observed, and identified as indicolite—as the name suggests, a blue variety
of tourmaline. Longer study and special analysis disclosed its real
composition and identity. It was the rather rare silicate of aluminum
known under the name dumortierite.
This mineral was at first regarded as kyanite and
later referred to hornblende, rhaetizite, and tourmaline. It is of a
beautiful blue, and in strict prismatic examples verges into grayish
green. It penetrates quartz and feldspar.
The carbonate of iron (siderite), formed
in pea-like concretions, is found sprinkled over the gneiss, in places
of a dark-brown to yellow color, and has arisen from the decomposition
of pyrite. It makes curious and attractive cabinet specimens.
Mr.
S. C. H. Bailey, a pioneer explorer in the mineralogy of the island,
has enthusiastically remarked of its mineral wealth that, " To one not
familiar with the mineralogy of that island, it will seem scarcely
credible that a larger number of species have been found upon it than
at the famous Lamoe Rock of Norway, or in the prolific mines of
Arendahl; larger than the noted lists of those found at Haddam or
Franklin, or any single locality in the United States."
Note.—The
teachers acknowledge their bewilderment before apparently deceptive
variations of a mineral species. They confess to a sense-of
despondency and despair, when having fixed an association of color and
structure with the name of a mineral, and they find variety and
instability. This discouragement is natural, but it will be short-lived
if the teachers continue their studies. Gradually from amid the
impressions of a mineral a series of typical images will emerge, which
will mark its ordinary and typical form, and around these the varieties
will group themselves with the relative hardness, the usual color, and
if possible the crystalline form, and despite changes in color or
texture they will find a mineral preserves a reasonable identity under
all variations.
The
varieties will eventually add a new charm to the subject, and they will
become a new element of interest. By constantly collecting and
observing, and resorting for assistance to some expert for aid, they
will find the subject becomes more and more clear, fixed, and definite.
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