. The Canadian field-naturalist. Natural history. September, 1918] The Ottawa Naturalist 51 It will be noted that the Miller-Bravais symbols used in this table are not the same as those given in the Winkeltabellen for the corresponding angles. This is due to the difference of orientation, Gold- schmidl usmg for the tourmaline an orientation G., in which the crystal has been turned 30 around the vertical axis, from Dana's orientation G-. If ghkl and g'h'k T are the Miller-Bravais symbols of a certain face, respectively in the orientations G, and G„, those symbols are related by the following eq
. The Canadian field-naturalist. Natural history. September, 1918] The Ottawa Naturalist 51 It will be noted that the Miller-Bravais symbols used in this table are not the same as those given in the Winkeltabellen for the corresponding angles. This is due to the difference of orientation, Gold- schmidl usmg for the tourmaline an orientation G., in which the crystal has been turned 30 around the vertical axis, from Dana's orientation G-. If ghkl and g'h'k T are the Miller-Bravais symbols of a certain face, respectively in the orientations G, and G„, those symbols are related by the following equations: g = h'-k' h = k'-g' k = g'-h' 1 = 1' Example: g'h'k'l'= I 120 g=|+2=:3 h=2—1=3 k=l—1=0 1=0 ghkl = 3300=1100 The calculated angles of Goldschmidt are based on Miller's ratio c = The tourmaline from Baffin Land has a slightly different parameter. We may calculate this from the measurements made on the terminal faces, which gave very good or good reflections, by applying the formula: . ^ v' 3 ^ tan p 2 Jg' + r- + oh The results are indicated in the following tabic Number of the face Letter Reflections Symbol p c. 17 u vg 3251 66 2\' 21 0 g 2201 46 07 25 o vg 0221 46 18 24 P vg lOTi 27 37 25 P vg TlOl 27 35 26 P vg oTii 27 28 27 e g lT02 14 30 In order to calculate the average value of c, we omit the exceptional value found from the measure- ments made on face 27 and take the average of the first six values of c. This leads us to: c = Such a high value of c indicates that the tourma- line from Baffin Land probably contains ferric oxide Fe.,0,, a fact that is emphasized by the dark green color. Tourmalines containing alkalis, magnesia or ferrous iron show a vertical parameter smaller than and their color is lighter. A chemical analysis could not be performed on account of the small dimensions of the crystal. The correspondence between the measured angles and the calculated angles of Goldschmi
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