1890.] Mineralogy and Petrography. 69 
MINERALOGY AND PETROGRAPHY.' 
Petrographical News.—A most interesting rock is described by 
Osann? as forming the body of the hill known as Hoyazo, in the 
Spanish Province Almeria. The rock is an andesite consisting of a 
ground-mass of colorless glass containing small crystals of cordierite, 
flakes of biotite, lath-shaped microlites of plagioclase, and of an 
orthorhombic pyroxene, in which are porphyritic crystals of labradorite, 
a large quantity of biotite, columnar crystals of bronzite, hornblende, 
augite, and cordierite. The last-named mineral occurs in the form of 
irregular grains associated with quartz, and also in well-developed 
crystals, with a pleochroism: 4 = yellowish-white ; B= dark violet ; 
C= light violet. In therock are inclusions of quartz, of aggregates 
of quartz and cordierite, and of a biotite gneiss rich in cordierite and 
garnet. A portion of the cordierite, separated from the rock, was 
analyzed with this result : 
SiO. ALO,- F60; FeO o MnO -M Sp. Gr, 
48.58 32.44 af 037 tr 6.03 2.625—2.628 
The mineral is usually fresh, but contains numerous inclusions of silli- 
manite, whose composition is: AlO, = 63.52 %, SiO, = 35-43 f- 
The granular cordierite is supposed to represent the remains of foreign 
inclusions in which the mineral was an original constituent. crys- 
tallized variety is thought to have arisen from the solution of a portion 
of the inclusions and a subsequent re-separation of cordierite, as well- 
developed crystals. The author regards the same explanation as ap- 
plicable to all the cases in which cordierite has been found in volcanic 
rocks, 7.¢., it is a secondary mineral produced by the solution of for- 
eign inclusions in the magma of the eruptive. Lacroix ê intends to 
make a complete study of pyroxene gneiss, and of rocks containing 
scapolite. He has published the first results of his work in a very 
excellent paper which is occupied with descriptions of the rocks of 
these two classes, together with the rocks associated with them as they 
are found in Brittany and in other parts of France, in Saxony, Austria, 
Spain, Algeria, Norway, Sweden, New York, Canada, Ceylon, per 
and a few other places. As is to besexpected, Lacroix finds m 
interesting facts connected with the structure, composition and peed 

1 Edited by Dr. W. s. Bayley, Colby University, Waterville, Me. 
2 Zeits. d. deutsch. geol. Gesells., XL., 1888, p. 694. 
3 Bull. Soc. Franc. d. Min., XILI., 1889. 0. 83. 

