478 LARSEN AND HUNTER: MELILITE 



Z > X, Its index of refraction is 2.34 and its birefringence, 

 about 0.002. In thin sections it is distinguished from the garnet, 

 which is also common in the rocks, by its sUghtly different color 

 and especially by its weak birefringence and twinning, which is 

 uniformly present except in a few of the very small crystals. 



TITANIFEROUS ANDRADITE 



Black andradite garnet is present in most of the igneous rocks 

 of the Iron Hill area but is especially abundant in the rock 

 related to ijolite and locally is an important constituent of the 

 soda syenite. Specimens of a soda syenite collected from near 

 the contact with the pyroxenite on the southeast slope of the 

 knob 9500' + north of North Beaver Creek are made up of micro- 

 perthite and somewhat less garnet which is interstitial to the 

 feldspar. The garnets are commonly about a millimeter across, 

 are anhedral, black, and of submetallic luster. In thin sections 

 they are dark reddish brown and are not very different from some 

 of the perofskite for which they were at first mistaken. Their 

 index of refraction was measured by the imbedding method and 

 found to be 1.907 ± 0.005. . 



An approximate analysis of the garnets was made by W. T.. 

 Schaller of the Geological Survey with the following results: 



TABLE 2 

 Approximate Analysis of Titaniferous Andradite 



The analysis shows that the garnet is an andradite rather 

 high in titanium. A similar garnet is an important constituent 

 of the ijolite and locally it is the chief dark mineral. Some parts 

 of the ijolite are made up of coarse anhedral garnet and nephe- 



