Chemical Examination of American Minerals. 65 



21. BROWN MANGANESIAN GARNET. 



This mineral was sent me by Dr. Torrey, under the name 

 of brown manganesian garnet. Its locality is Franklin, Sussex 

 County, New-Jersey. 



Color tombac-brown. 



Texture granular, because the specimen consists of a con- 

 geries of imperfect crystals. Some of these crystals appear 

 to be octahedrons, either complete, or wanting their apexes. 

 Some are four-sided oblique prisms, terminated by four-sided 

 pyramids. One of these prisms was measured. Its angles 

 were about 111° and 69°. 



Scratched with difficulty by quartz. 



Brittle and very easily frangible. 



Lustre glistening, except some crystaline faces, which are 

 splendent. Resinous. 



Nearly opaque, or only translucent on the edges. 



Specific gravity 3-829. 



The constituents of this mineral were found to be. 



Silica, ------ 33-716 



Lime, ---_.. 25-864 



Alumina, ------ 7-972 



Protoxide of iron, - - - - 15'S40 



Protoxide of manganese, - _ _ J 6-704 



Water. ------ 0-080 



100-196 



This corresponds with, 



5 atoms silica, 



2 atoms lime, 



1 atom protoxide of iron, 



1 atom protoxide of manganese. 



So that the mineral would appear to be a compound of, 

 Vol. III. 9 



