MINERALOGY. 77 
nearly all traces of the triclinic feldspar has disappeared, and a green 
rock, with nearly the composition of epidosite, is the result. Examples 
of this are to be found in Cornish and Stewartstown, where all stages 
of the progress of alteration can be seen. In the eruptive diabases, 
epidote, resulting from alteration, often fills amygdaloidal cavities. Pro- 
ducts that result thus from decay rarely possess any definite crystalline 
outlines in the rocks; and this is the case with epidote, which commonly 
exists in very minute grains, or aggregates of grains. 
51. Zois1TE [H? Ca’ Al’ Sif OF] 
Zoisite differs from epidote in containing but little or no iron. It 
has been found in ash gray, much compressed, and deeply striated crys- 
tals at Westmoreland. It has also been found at Hanover, Franconia, 
and Lisbon. 
52. IotirE [Mg’ (Fe’, Al’)? Si O¥]. 
Very fine specimens of this beautiful mineral are found at Richmond. 
It occurs in the quartz rock and mica schist. Its color is blue, but its 
dichroism is very marked,—one species being blue when the light passes 
in the direction of the vertical axis, and brownish-violet when it passes 
at right angles thereto, the two colors obtained parallel to the two lateral 
axes being not markedly different. This mineral was found in opening 
a soapstone quarry. Iolite is also found in Unity and Croydon. This 
mineral alters with the greatest ease, the first result being the hydration 
af the mineral, then the separation of the prism by planes parallel to its 
base, and, finally, the production of a hydrous silicate, which varies much 
in composition. 
Tolites from Richmond and Unity have been analyzed by Dr. Jackson, 
with the following results : 
Richmond. Unity. 
Silica, . r 3 5 3 - - - 5 48.00 48.15 
Alumina, ; - . 3 F ‘ ‘ ‘ 35. 32.50 
Iron protoxide, 3 : 7 : F : , 6. 7.92 
Magnesia, % , . : ‘ 3 5 10. 10.14 
Manganese protoxide, . é a ‘i 5 : I. -28 
Water, . 5 : ‘ 7 : : . fe  ahewg -50 
100.00 99-49 
