274 The A?nericafi Geologist. November, i9ijii 
Calcite. In highly altered areas calcite is often quite con- 
spicuous among the decomposition products. It never shows 
crystal outline, occurring in patches wholly irregular. 
Pemiinite occurs only rarely, the ordinary product of chlo- 
ritization being clinochlore. The two chlorites can be distin- 
guished in this rock only by the weaker birefringence of the 
penninite which usually gives the "ultra blue" color between 
crossed nicols. 
Clinochlore is sometimes fibrous,' but oftener lamellar. It 
has perfect cleavage parallel to the base /(loo) to which fig is 
nearly perpendicular. The color in mass is grass green, in 
thin section pale green with weak pleochroism as follows: 
/ig =pale greenish yellow 
;/m=yellowish green 
//p - green. 
The absorption formula is the following: tif, <«m<'"p- 
The birefringence is about .010, and is distinctly greater 
than that of labradorite. 
Clinochlore occurs very often as an alteration product of 
the pyroxene, and more rarely of the labradorite. 
Mesolite occurs quite commonly at Carlton peak, in a man- 
ner showing most clearly its direct derivation from the labra- 
dorite, "according to the method previously described. Meso- 
lite is always fibrous, and often radially arranged. It has not 
been found at the Minnesota locality in fibers large enough to 
permit any determinations; through the courtesy of Prof. La- 
croix, a few acicular crystals collected by M. Gentil at Tak- 
dempt, Algeria, were examined. They are very rich in faceb 
of the vertical zone, four occurring between ;/z(iio) and 
hi' {no) contiguous. A measure of the zngXemm'iiio) A(iio) 
from a crystal giving unusually distinct and excellent images 
from both these faces gave the following result:* 
;;////' (no) A (no) =91" 35' 
The angle between ;«(no) and another well developed face 
of the vertical zone was: ///,r=i57^ 20'. 
Mesolite has two good cleavages parallel to rii(iio); its 
*M. Gentil found on crystals from the same locality f//m' (iio)A 
(iio)=9i° 22': See Lacroix: Mineralogie de la France. II. p. 276. 
