474 LARSEN AND HUNTER: MELILITE 



proposed were found in the drainage of Beaver Creek, in all, 

 covering an area a little less than a square mile. The largest of 

 these is between the forks of Beaver Creek; others are south of 

 the main Beaver Creek, The rock of these bodies is about two- 

 thirds or more melilite with considerable pyroxene, magnetite, 

 perofskite, and apatite, and in places biotite, calcite, and other 

 minerals. It varies greatly in texture but is commonly coarse, 

 and cleavage pieces of melilite a foot across are not uncommon. 

 The finest grained rock is hypidiomorphic granular with crystals 

 averaging 1 mm. across. In the coarser rock the luster of the 

 giant melilite individuals is mottled by large included crystals 

 of the other constituents. The melilite is anhedral so far as 

 observed. 



Physical properties. The mineral has a rather perfect basal 

 cleavage, which is better developed in some specimens than in 

 others. Its hardness is about 5. The specific gravity of the 

 analyzed specimen is 2.98. 



Optical properties. The pyroxene and ore are somewhat irregu- 

 larly distributed in the large melilite crystals so that considerable 

 sized fragments of melilite can be obtained nearly free from 

 inclusions. The melilite is nearly colorless, to gray, and has a 

 noticeably greasy luster. Splinters are clear and transparent 

 but carry scattered, minute inclusions of opacite — probably mag- 

 netite. The gray color and lack of transparency of rather thick 

 masses are due to these inclusions. In thin sections the melilite 

 is colorless, and contains large crystals up to several centimeters 

 across of pyroxene, apatite, calcite, magnetite, and perofskite 

 in addition to the minute inclusions of opacite which are com- 

 monly collected in irregular areas or streaks. In the finer-grained 

 rocks, sections of melilite with the maximum birefringence show 

 a well-developed cleavage (001). Powdered fragments of the 

 mineral commonly lie on the basal cleavage and hence are nor- 

 mal to the optic axis. The mineral is uniaxial and negative. 

 The indices of refraction were measured on two polished plates 

 from the analyzed specimen and also on polished plates from 

 two other specimens from different outcrops. The following 

 values were found: Coarse,, analyzed material. coNa = 1.6319 and 



