1890.] Mineralogy and Petrography. 1073 
Mineralogical News.—In two very much decomposed rocks 
from Custer County, Colorado, Mr. Cross Y has discovered an interest- 
ing series of secondary horndlendes and pyroxenes, whose study leads 
him to the view expressed by Williams, viz., that the most con- 
venient way to place hornblende crystals in order to show their rela- 
tions to pyroxene is with the orthodome in the position of the basal 
plane. One of the amphiboles described is a blue variety with the pleo- 
chroism of glaucophane. It is found in a rock composed of green 
pyroxene and small pieces of brown hornblende, imbedded in a ma- 
trix of quartz, calcite, and minute blue and green amphibole needles. 
It is an alteration product of the brown hornblende and the augite, 
from both of which it results either directly or through the interposi- 
tion of actinolite. Both the latter mineral and the blue hornblende 
are also found as enlargements attached to the clinopinacoidal and 
terminal planes of the brown hornblende and the augite. The axis 
of greatest elasticity of the blue hornblende is inclined 13? to 15? to 
the vertical cleavage, and is on the same side of it as in the case of 
glaucophane, actinolite, etc., while in common hornblende it is on the 
opposite side, since the extinction angle. is here the angle included be- 
tween c and the axis of least elasticity. The optical angle of the blue 
amphibole is large, and the absorption is 4» B> C. A second rock 
in which the mineral occurs is a conglomerate, in pebbles in which 
the same relations exist between the hornblendes as those mentioned. 
A second rare variety of amphibole discovered in these rocks is of a 
rich chestnut-brown color, and has an extinction of 8°. It is regarded 
as an added growth. An emerald-green secondary augite occurs in 
s pebbles in the conglomerate above mentioned. It is an altera- 
tion product of the blue hornblende and of an unknown yellow mine r 
Its axis of greatest elasticity is but slightly inclined to e. Its pleo- 
chroism is strong in green and yellow tints, and its absorption as fol- 
lows: 4» B> C. Upon comparing the properties of these minerals 
with those of other members of the amphiboloid group Mr. Cross is 
inclined to regard the chestnut-brown hornblende as closely allied to 
barkevicite, while the blue variety is either arfvedsonite or riebeckite, 
The green augite is considered to be @gerine or acmite. Twelve dia- 
grams exhibiting the relations of the axes of elasticity to the crys- 
tallographic axes of the different varieties of amphibole and pyroxene 
accompany the article. If the plane usually taken as the orthodome 
in ionnad and augite is made the basal plane, the relations shown 
by the diagrams are rendered quite simple; whereas if the usual 
10 Amer. Jour. Sci., May, 1890, p. 359. 
