1893.]* Mineralogy and Petrography. 1005 
the microcline of these, so that around each grain of the mica is a zone of 
pellucid feldspar, and on both sides of veins of the sericite are clear 
borders of microcline entirely free from inclusions of any kind. 
Chalcedony and other Silicious Spherulites.—A well-illus- 
trated article by Levy and Meunier-Chalmas" treats of various forms 
assumed by the molecule Si O, in the production of spherulites. Chal- 
cedony has heretofore been regarded as a mixture of quartz and opal. 
The present authors have had an opportunity to study some excellent 
specimens of silica spherulites and concretions from the gypsum beds 
in the Paris Basin. Chalcedony and two new forms of silica, called by 
the authors quartzine and lutecite, are the components of these concre- 
tions. All three of these substances are fibrous forms of the same min- 
eral, which is positive and biaxial, with an optical angle varying 
* between 20°-35°. Thus they are different from quartz. The distinc- 
tions between the three varieties rest upon their habit. Chalcedony is 
elongated parallel to the base of the crystals, and quartzine par- 
allel to the plane of their optical axis, while the lutecite fibers 
are elongated in a direction making an angle of 29? with the opti- 
cal axial plane. The relation of the long axis of each variety to 
the optical constants of the mineral is carefully worked out, and the 
appearances of thin sections of their groupings are Hhotzsad by eight 
beautifully executed photographs. 
Petrographical News.—Andrea and Osann" ascribe the exist- 
ence of a porphyry breccia at Dorsenheim near Heidelberg to the 
erushing of porphyry by faulting and the cementing together of the 
fragments thus made by siliceous material. 
A series of high dipping crystalline schists near Salida, Col., is re- 
garded by. Cross? as having originated by the alteration of great flows 
of basic and acid lavas erupted in Algonkian time. Though the rocks 
are now hornblende and micaceous schists, some of them still present a 
few of the structural features of diabases and porphyries. 
Danalite from Redruth, Coriwali .—Tetrahedra of danalite at 
Redruth, Cornwall, are associated with quartz and arsenopyrite. 
Miers" mentions them as projecting from a layer of massive danalite 
with a thickness of from a quarter to half an inch. Some of the crys- 
10 Bull. Soc. Franc d. Min., xv, p. 159. 
11 Mitth. gross. Badisch. geol. Landesanst, ii, p. 365. 
x Col. Sci. Soc. Jan. 2 2,1893 
18 Miner. Magazine, x, p. 10. 
