File:Birds and nature (1901) (14745377571).jpg

Identifier: birdsnature9101unse (find matches)
Title: Birds and nature
Year: 1900 (1900s)
Authors:
Subjects: Birds Natural history
Publisher: Chicago, Ill. : A.W. Mumford, Publisher
Contributing Library: University of Illinois Urbana-Champaign
Digitizing Sponsor: University of Illinois Urbana-Champaign

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distinguished from this in the following manner: On fusing the powdered mineral with a mixture of bisulphate of potash and fluor spar (best done on a little loop of platinum wire) Tourmaline will color the flame green, while Hornblende will produce no coloration. The black opaque crystals often reach a large size, as some are known to be four feet in length. Both black and brown Tourmaline are usually opaque, and hence have no value as gems. The Tourmalines available for gems are transparent and have a great variety of color. The gem Tourmalines are to be found in only a few localities. They occur in Maine, Connecticut and California in our own country, and also in Brazil, Russia and Ceylon. The crystals are usually in the form of long, slender prisms. They often have the peculiarity of being differently colored in different portions. Thus a crystal may be green at one end and red at the other, and in cross section may show a blue center, then a colorless zone, then one of red and then one of green. 74
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mm* UNWERSm Of ILLiNUri Some of the crystals from Paris, Me.,change from white at one termination toemerald green, then light green, thenpink, and finally are colorless at the othertermination. In some crystals again thered passes to blue, the blue to green andthe green to black. Exactly what produces these differ-ences of color is not known. It is knownthat black Tourmaline has an excess ofiron, the red and green an excess of so-dium and lithium, and the yellow andbrown an excess of magnesium in theircomposition. These same differences ofcomposition characterize similar colors inportions of the same crystal as well asseparate crystals. Hence the evidence isquite conclusive that the color in someway depends on the composition. Manytransparent Tourmalines, while appear-ing of a uniform color when viewedin any one direction, exhibit different col-ors when viewed in different directions.Thus, one of the long, slender crystalsmay appear green when held lengthwisein from of the eye, but wh

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