AET. 18 MINERALS OF ITALIAN MOUNTAIN CROSS AND SHANNON 23 



corroded crystals of the first tj^pe contain silky white fibrous ma- 

 terial having the appearance of a zeolite. This is grown upon the 

 vesuvianite crystal parallel to the vertical axis and apprently is 

 replacing it. About 5 specimens show this material. When ex- 

 amined under the microscope the fibers are thin and of such ex- 

 tremely low birefringence that only very thick bundles are visible 

 under crossed nicols. They have parallel extinction, positive elon- 

 gation and a refractive index, approximately, of 1.717. The ma- 

 terial of the fibers is evidently also vesuviante. 



EPIDOTE 



Epidote forms well terminated crystals varying somewhat in size, 

 in cavities in anorthite, imperfect green or greenish-yellow columnar 

 or acicular masses resting upon vesuvianite or on well developed 

 diopside crystals and in cavities in massive diopside rock, between 

 large grossularite garnets or in calcite veinlets cutting hornfels and 

 altered shale. 



The largest group of epidote-bearing specimens is that which has 

 been mentioned beyond as consisting of anorthite cores partially 

 replaced by adularia and containing numerous cavities in which the 

 epidote occurs in crystals associated with titanite crystals, limonite 

 pseudomorphs after pyrite, and scaly aggregates of chlorite. 

 Many of the cavities are molds of a prismatic mineral of unknown 

 identity which was removed before the later minerals were deposited. 

 (No. 84560.) The epidote crystals vary in size from minute and 

 comparatively perfect prisms with good terminations to a maximum 

 observed size of 1 by 2 centimeters and the color varies from green- 

 ish-yellow to greenish-black. The mineral of one specimen of this 

 lot was found to be biaxial and negative with 2V medium large, 

 dispersion, r > v, strong. The refractive indices were roughly 

 a= 1.722, ^=1.730, 8 = 1.755. 



Another specimen shows an almost solid mass of epidote resting 

 upon coarse vesuvianite. Cavities in this contain epidote crystals, 

 which are rude prisms, deep yellow-green inside and light greenish- 

 yellow outside. The suggestion of zoning in composition, obtained 

 from the color distribution in these imperfect crystals is confirmed 

 by their optical properties. When a whole crystal is crushed the 

 grains are found to be biaxial negative, ( — ), with 2V varying 

 from medium to large. The dispersion, r < v, varies from per- 

 ceptible to strong, and the 13 index ranges from about 1.720 to 1.740, 

 The grains show some twin lamellae. This powder gave no fluorine 

 reaction in a closed tube with potassium bisulphate. 



