May, 1906. Lower CaLiFoRNIA ZOISITE—FARRINGTON. 7 
calcium. No further investigation was made of this point, however. 
Although the formula of zoisite is usually considered to be H, Ca, Al, 
Si, O,,, other analysts have obtained percentages which indicate 
that an additional molecule of water is present. This is true, for 
instance, of the analyses of zoisite from Fuschthal and Traversella 
quoted by Dana.* The high temperature required to drive off the water 
from the Lower California mineral seems to preclude the possibility 
of its being present as the result of alteration, as might otherwise 
be assumed. The amount of iron in the zoisite shown by the analysis 
is high for this mineral and approximates that afforded by epidote. 
The mineral with which the Zoisite is associated is, as stated, 
white and granular. In cavities it exhibits minute imperfect crystals 
which have a distinct, pearly luster when fractured. The blowpipe 
and other characters of this mineral indicate it to be prehnite and a com- 
parison with fragments kindly furnished by Dr. W. T. Schaller leaves 
little doubt that it is the same mineral analyzed ¢ by him and found 
to be prehnite. Its association with zoisite is of interest owing to the 
similarity in composition of the two minerals. The prehnite seems 
generally to furnish a matrix which the zoisite penetrates, but occa- 
sionally it coats the zoisite groups in such a way as to suggest that it 
is an alteration product of the latter. The unusual features of the 
zoisite seem to be therefore, its radiating habit, its high content of 
water and iron and its association with prehnite. 
Through the kindness of Prof. L. P. Gratacap of the American 
Museum of Natural History, the writer was permitted to study two 
specimens of zoisite in the collection of that institution which were 
undoubtedly from the same locality as the above. They have the 
more usual ash-gray color of zoisite and the grouping of the crystals into 
cones is only partial. For the most part the crystals occur in hemi- 
spherical cavities which were, in the specimens studied, about three 
inches in diameter. The crystals interlace these cavities with great 
variations of size and direction. Many of the crystals are quite 
minute. All are from acicular to bladed in habit. Although some 
crystals have free terminations, no end faces could be discerned. 
These specimens show that grouping into cones is not constant for the 
zoisite from this locality but its occurrence at all is noteworthy. 
| * System of Mineralogy, 6thed., p. 514. 
+ Bull. U.S. Geol. Survey No. 262, p.128 
