W. E. Ford — Optical Study of the Amphiboles. 181 



10 



Hornblende from Edenville, Orange Co., New York, 

 a = 16583, ft = 1-6701, y = 1-6789. Mean index = 1-668. 

 y— a= -0206. 

 2V=81°42'. c>c' = 23°48'. 

 Pleochroism, o and b = light brownish green, c = dark green. 

 Absorption, c > b = a. 

 Hornblende from Renfrew, Ontario, Canada. 

 Mean index = 1-67. c ^ c = 33° 20'. 

 Pleochroism, o and 6 = olive-green, c = dark blue-green. 

 Absorption, c > b > a. 

 Hornblende from Mte. Somma, Italy. 

 Mean index = 1-68. 



Pleochroism, a and b = olive-green, c = dark blue-green. 

 Absorption, c b = a. 



Hornblende from Cornwall, Orange Co., New York. 

 Mean index = 1*71. CaC=9°. 

 Pleochroism, a = light olive-green, b = yellowish green, 



c = bluish-green. 

 Absorption, c > b > a. 



9 



10 



Si0 2 



57-45 



5769 



54-80 



56-25 



52-31 



51-85 



4199 



43-76 



39-48 



36-86 



Ti0 2 





0-14 



010 





0-28 



1-26 



1-46 



0-78 



0-30 



1-04 



A1 2 3 



1-30 



1-80 



2-58 



1-24 



2-69 



4-36 



11-62 



8-33 



12-99 



12-10 



Fe 2 3 



0-18 



00 



2-50 



0-78 



3-09 



2-58 



2-67 



6-90 



7-25 



7-41 



FeO 



0-22 



0-55 



4-75 



5-50 



6-68 



5-46 



14-32 



10-47 



10-73 



23-35 



MnO 



0-07 



tr. 



tr. 



0-48 



0-70 



0-35 



025 



050 



1-00 



0-77 



MgO 



24-85 



2412 



20-30 



21-19 



19-27 



19-48 



11-17 



12-63 



11-47 



1-90 



CaO 



12-89 



13-19 



12-08 



12-08 



11-88 



10-60 



11-52 



9-84 



12-01 



10-59 



K 2 



0-54 



022 



24 



0-28 



0-50 



035 



0-98 



1-28 



2-39 



3-20 



Na 2 



067 



0-48 



0-82 



0.19 



0-78 



2-15 



2-49 



3-43 



1-70 



1-20 



H 2 



1-16 



1-56 



1-60 



1-81 



1-42 



1-21 



061 



0-65 



0-76 



1-30 



F 2 



0-77 



0-37 



0-77 



0-04 



0-93 



0-46 



0-80 



1-82 



0-05 



0-27 



Loss at 110° 09 



o-io 



o-ii 





0-08 



0-13 



0-08 



010 



0-12 







100-19 



100-22 



100-65 



99-84 



100 59 



100-24 



99-96 



100-49 



100-25 



99-99 



0=F 2 



0-32 



0-15 



0-32 





039 



0-22 



0-33 



0-76 



002 



0-11 



99-87 100-07 100-33 



100-20 100-02 99-63 99-73 100-23 99-88 



All analyses by Stanley except No. 10, which is by J. L. Nelson. 



1. Tremolite from Richville. 



2. Tremolite from Lee. 



3. Actinolite from Russell. 



4. Actinolite from Greiner. 



5. Actinolite from Pierrepont. 



6. Actinolite from Kragero. 



7. Hornblende from Edenville. 



8. Hornblende from Renfrew. 



9. Hornblende from Mte. Somma. 

 10. Hornblende from Cornwall. 



From the above facts it is possible to make the following 

 general statements concerning the optical character of what 

 may be called normal and typical amphiboles. The mean 

 index of refraction ranges from about 1*61 to about 1*71. 

 The mean index of refraction of typical tremolite lies between 

 1 - 61 and 1*62 ; that of typical actinolite ranges from 1*63 to 



