Notes on Some Rocks and Minerals— Emerson. 97 
*This article was written many years ago and mislaid. Since 
then the question of the cause of the blue quartz so common in 
the Archaean has interested me and this quartz is so generally 
without inclusions and strongly strained that I have considered 
the color to result from this strain, especially since the blue color 
can be sometimes seen to disappear when the strain is relieved 
by Assuring. So long ago as 1822 Cleveland cites many localities 
of the mineral. It is found in Bohemia, Macedonia, etc.; in the 
United States; in Virginia: near the Blue Ridge, in Amherst and 
Campbell counties in amorphous masses (T. D. Porter). In Penn- 
, sylvania: Chester county; and near Abington, Montgomery county, 
is found an amorphous blue quartz (Seybert). About two miles 
west from West Chester, it contains zircon (Lea). P. Cleaveland, 
(Treatise on Mineralogy and Geology, 2d Edition, 1822, I, p. 237.) 
Keith reports it from the Catoctin belt as the constant ac- 
companiment of the pre-Cambrian granite in a small portion of its 
extent. At certain points the blue quartz granite is not peculiar 
microscopically, but is macroscopically striking from the brilliancy 
of its color. The blue quartz is in original crystals and in veins 
and patches. 
I have found the mineral everywhere characteristic of the pre- 
Cambrian rocks of western New England and western Sweden. In 
eastern central New England post-Carboniferous blue quartz gran- 
ites occur and I have recently described beautiful pre-Carboniferous 
blue quartz porphyries from East Greenwich, R. I. I have seen 
similar porphyries in Finland. 
It is curious that this deepest colored blue quartz should con- 
tain cobalt ores, deep blue spinel and the rich blue dumortierite. 
The two last may contribute to the blue color making it deeper 
than usual but they do not explain the phenomenon in its wider 
appearance. 
The broad biotite-dumortierite border seems to have 
been formed by the solvent action of the heated alkali-silica 
solutions, and then to have been in large measure resorbed. 
Spots of millerite spread through the rock in thick 
curved sheets as if it replaced the mica. It gives with the 
blowpipe reactions for sulphur and nickel alone, has H. 3.5, 
is very brittle and gives a dark streak. Exceptionally large 
cleavage pieces a quarter of an inch across were obtained. 
The cleavage is nearly perfect parallel to a rhombohedron 
of 144 degrees 15 minutes a mean of several measurements 
with reflecting goniometer. The color is bright brass yel- 
low. 
• An. Rep. U. S. G. S., xiv, p. 300, pi. xxlv. 
