Buddington — Natural and Synthetic Melilites. 73 



garnets. Many attempts have been made to synthesize 

 grossularite, usually without success. Shepherd and 

 Rankin, 17 however, describe the formation of grossnlarite 

 by the action of alnminnm chloride upon calcium ortho- 

 silicate heated with water under pressure in a steel bomb 

 at a temperature of 400° ±50°. 



Artificial glass of the composition of grossularite was 

 crystallized for 16 hours at 980° and gave an unidentified 

 fibrous aggregate of moderate birefringence in which at 

 least two different compounds are present. At the 

 eutectic or melting point (1265°) it forms a mixture of 

 gehlenite, anorthite, and pseudo-wollastonite.. 



Grossularite held for possible inversion or dissociation 

 for 166 hours at 800° and for 16 hours at 1100° was 

 unchanged. 



Sarcolite. 



The composition of the mineral sarcolite is usually 

 expressed as 3(9Ca.Na 2 )O.Al 2 3 .3Si0 2 , and the crystal 

 system is tetragonal. The indices of refraction given by 

 Zambonini 18 are w tt = 1.6035 and n £ = 1.6147, and the 

 density 2.92. The mineral is optically positive. 



Bladed crystals formed by crystallizing a synthetic 

 mixture of the same composition for 16 hours at 1000° 

 have the indices n a = 1.631 ± 0.005 and tie = 1.615 ± 

 0.005 ; the optical character being negative and the crystal 

 system tetragonal. Thus the indices of refraction of the 

 artificial crystals do not agree with those of the natural 

 sarcolite, and the optical character is different so that 

 the artificial crystals must be a polymorphic form, though 

 crystallizing in the same system. 



To test for possible inversion phenomena, a specimen 

 of sarcolite from Monte Somma, obtained from the U. S. 

 National Museum, was subjected to a series of heat treat- 

 ments. The mineral was held for 156 hours at 700°, 166 

 hours at 800°, 96 hours at 1000°, and 4 hours at 1100° 

 without showing a trace of alteration except in an occa- 

 sional grain. In a few grains the alteration observed 

 might be interpreted as indicating inversion, but the 

 natural mineral could not be obtained in absolute purity 



1T E. S. Shepherd and G. A. Kankin, this Journal, 28, 305, 1909. 

 1S F. Zambonini, op. cit., p. 247. 



