. Birds and nature . distinguished fromthis in the following manner: On fusingthe powdered mineral with a mixture ofbisulphate of potash and fluor spar (bestdone on a little loop of platinum wire)Tourmaline will color the flame green,while Hornblende will produce no col-oration. The black opaque crystals often reacha large size, as some are known to befour feet in length. Both black andbrown Tourmaline are usually opaque,and hence have no value as gems. TheTourmalines available for gems are trans-parent and have a great variety of color. The gem Tourmalines are to be foundin only a few localit
. Birds and nature . distinguished fromthis in the following manner: On fusingthe powdered mineral with a mixture ofbisulphate of potash and fluor spar (bestdone on a little loop of platinum wire)Tourmaline will color the flame green,while Hornblende will produce no col-oration. The black opaque crystals often reacha large size, as some are known to befour feet in length. Both black andbrown Tourmaline are usually opaque,and hence have no value as gems. TheTourmalines available for gems are trans-parent and have a great variety of color. The gem Tourmalines are to be foundin only a few localities. They occur inMaine, Connecticut and California in ourown country, and also in Brazil, Russiaand Ceylon. The crystals are usually inthe form of long, slender prisms. Theyoften have the peculiarity of being differ-ently colored in different portions. Thusa crystal may be green at one end andred at the other, and in cross section mayshow a blue center, then a colorless zone,then one of red and then one of green. 74. 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 , one of the long, slender crystalsmay appear green when held lengthwisein fr
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