IDENTIFICATION OF GEMS BY THE MICRO SPECTROSCOPE.
Attention
has again been called to the use of the microspectro-scope in the
identification of gem minerals in a paper by Edgar T. Wherry.1 Dr.
Wherry mentions the discussions of this subject in textbooks and other
publications and supplements them with notes on methods of
microspectroscopic examination and tables of results on many minerals
examined including gem minerals. Of the other articles cited, one by F.
J. Keeley2 contains interesting data on the color and the coloring agents of several gem minerals.
The
apparatus used by Dr. Wherry "consists of a Crouch binocular microscope
stand fitted with a 37-millimeter objective, an Abbe-Zciss 'Spectral
Ocular' in the right hand tube, and in the other an ordinary low-power
eyepiece, marked on the lower lens at the point where the image of the
mineral grain falls when it is visible through the spectroscope slit."
White Tight such as is given by a Welsbach burner surrounded by a dark
chimney is found preferable to sunlight. For the examination of gems,
either loose or set, it is desirable to concentrate the light from the
side by means of a lens or parabolic mirror. A gem must be transparent
or at least fairly translucent to respond to the test, since it is
necessary for the light to penetrate well into the mineral for
absorption of color to take place properly.
Colorless
gems show a continuous spectrum, but if the mineral is colored by
certain elements or chemical substances, light of some color will be
absorbed by it and dark bands will appear in the spectrum at places
which are learned to be characteristic of such elements. If the
coloring agent in different gems is known, a stone in doubt can be
examined for thepresence of that coloring agent by the
microspectroscope. Dr. Wherry has found this method useful in
determining the genuineness of rubies, sapphires, and emeralds, and in
picking out corundum, zircon, and garnet from gem gravels.
IMPORTS.
The
value of the imports of precious stones into the United States during
the calendar year 1914, as reported by the Bureau of Foreign and
Domestic Commerce, amounted to $19,211,084, the smallest since 1908,
when it was $13,700,404. The imports were less by 826,220,914 in 1914
than in 1913, the greatest proportionate decrease occurring in rough or
uncut diamonds. Large decreases were also recorded in pearls and cut
diamonds, and the only increase in value of imports was in glazier
diamonds.
The
following table shows the value of the diamonds, pearls, and other
precious stones imported into the United States from 1906 to 1914,
inclusive:
1 The microspectroscope in mineralogy: Smithsonian Misc. Coll., vol. 65, No. 5, Pub. No.2362,16 pp., 1915.
2 Microspectroscopic observations: Acad. Nat. Sci. Philadelphia Proa, pp. 106-116, 1911.
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