igoo.] SMITH— PARAGENESIS OF MINERALS. 195 



This corresponds to a mixed molecule, of approximately one- 

 half alumina-iron garnet (almandine), one-sixth alumina-magnesia 

 garnet (pyrope), and one-third alumina-lime garnet (grossular). 

 Titanium Minerals. — Sphene or titanite is abundant in small 

 patches, more rarely in crystals, in most of the glaucophane rocks, 

 but is especially characteristic of the more basic members of the 

 series. The titanium appears to have been derived chiefly from the 

 titaniferous hornblendes and pyroxenes of the original rocks. In 

 the only partly recrystallized diabases and gabbros, where the augites 

 have been uralited, or changed to actinolite or carinthine, the 

 titanium has not remained in the ferro-magnesian mineral, but has 

 separated out as leucoxene and titanite. In the partly recrystallized 

 quartz diorite of Oak Ridge the original titaniferous hornblende has 

 been changed on the borders to crossite, and the titanium has in this 

 case, too, crystallized out as leucoxene and titanite. The same 

 thing has been observed in a syenite of Spanish Peak in Plumas 

 County, where the hornblende has been partly changed to crocidolite. 

 In an orthoclase-glaucophane gneiss of Melitta sphene is abundant 

 in sharply defined rhombs in thin sections, probably derived in the 

 same way. 



Rutile is rather common in minute crystals in most of the basic 

 schists and eclogites, but in an eclogite from Coyote Creek near 

 San Martin it is abundant in large crystals of lo mm. in length. 

 Its genesis is probably the same as that of sphene. 



Lazvsonite, — This is one of the most characteristic minerals in 

 the glaucophane bearing rocks of California. It was first described 

 by F. L. Ransome,^ from the eclogite near Reed's Station on the 

 Tiburon Peninsula. It has since been found to be abundant in 

 schists, gneisses and eclogites from many parts of the Coast 

 Ranges, and has also been found in similar rocks in Europe. Since 

 it is such a constant companion of glaucophane, its occurrence and 

 origin throw much light on the genesis of that mineral. 



Lawsonite is orthorhombic in form, and of simple habit, the 

 prism (no) and the basal pinacoid (ooi) being the commonest 



^ " On Lawsonite, a New Rock-forming Mineral, from the Tiburon Penin- 

 sula, Marin County, Cal.," Bull. Dept. Geol. Univ. of California, Vol. I., No. 

 10 (1895), pp. 301-312. 



