well
developed in concentric layers, though generally the cavities are very
irregular in shape and inclusions. The walls of the cavities are
generally drusy with tiny brilliant crystals which Cross determined to
be sanadine. Small quartz crystals also occur in the cavities though
no tridymite has been found. The garnets have a transparent deep-red
to cinnamon-red color and are of the spessartite variety. Crystals of
over a centimeter in diameter are rare and the average size is about
2.5 millimeters. The crystals have sharp edges and brilliant faces in
the cavities. Generally only a part of the crystal form is developed,
for the surfaces are very rough where the garnet is attached to the
matrix. The predominant crystal form is the trapezohedron (211) with a
small development of the dodecahedron (110). Several garnets often
occur in the same cavity, with or without topaz. The topaz is less
plentiful than the garnet and of about equal dimensions. The crystals
are attached to the walls of the cavities and to the shells in
different positions, so that in some cases doubly terminated crystals
occur. The forms observed in the order of their prominence are given bv
Cross as: M(110), L(120), 0(221), C(001), F(021), Y(041), A(100),
G(130), and F(201). The crystals are clear wine pink or yellow while in
the unbroken cavities in the rock, but fade to colorless or tinted pale
bluish on exposure to the light.
Cross"
describes also a similar occurrence of garnet in a coarse rhyolite at
Chalk Mountain, near Fremont Pass, Colorado. A specimen of rhyolite
with small garnets in a cavity was given to the writer by Mr. J. D.
Endicott, of Canon City. This specimen was from the Gudger mine near
Westcliffe, Custer County, Colo., and appears to come from an
occurrence similar to that described above.
JADE.
BURMA.
The production of jade (jadeite) in the Myitkyina district of upper Burma during 1907 amounted to 3,590 hundredweight,6
with a local value of £18,998; "this is an increase of 1,375-1/2
hundredweight over 1906. Part of the jade is used locally, part carried
overland to southwest China, and the greater part is exported through
Rangoon, principally to China. The exports through Rangoon during 1907
amounted to 2,636 hundredweight, valued at £49,643. The production in
1908 was 3,367 hundredweight, valued at £22,332.c
The
occurrence and origin of jadeite in the Kachin Hills in the Myitkyina
district, upper Burma, has been carefully discussed by A. W. G. Bleeck.d
Jadeite is found at three places in the Kachin Hills, at Tawmaw, Hweka,
and Mamon. At Tawmaw the deposits consist of a metamorphosed igneous
dike intruded into serpentine. At Hweka the jadeite occurs in bowlders
in a conglomerate. The jadeite bowlders are quarried from the slope of
a hill and are sometimes found of large size. At Mamon the jadeite is
found in bowlders in the alluvial deposits and bed of Uru Chaung River.
a
Sanadine and topaz from Colorado: Am. Jour. Sci., 3d ser., vol. 27,
1884, pp. 94-96. 6 Rec. Geol. Survey India, vol. 37, pt. 1, 1908.
e
Advance statement of the production of minerals in India in 1908, by
the Director of the Geological Survey of India, June 10, 1909. d Rec. Geol. Survey India, vol. 36, pt. 4, 1908, pp. 254-285.
