30 Chemical Examination of American Minerals. 



Note. This is the substance mentioned by Dr. Fowler, in 

 the ninth volume of Silliman's Journal, p. 245 as crystallized 

 siliceous oxide of manganese. The crystals are six or eight- 

 sided prisms, with plane terminations, which are inclined to 

 the axis at an angle of about 108°. They are sometimes two 

 inches or more in length, and an inch in diameter. 



6. FERRUGINOUS SILICATE OF MANGANESE. 



I received this mineral about four years ago from Dr. 

 Torrey, under the name of silicate of zinc. The locality is 

 Franklin, in New-Jersey. 



Its external color was brown, with a slight shade of red. 

 The external lustre glimmering, the internal shining and semi- 

 metallic. 



The specimen consisted of a group of crystals very im- 

 perfect, their faces being dull and far from flat, and their 

 edges so much rounded, that it was very difficult to obtain 

 a correct notion of their form. They had the aspect of dode- 

 cahedrons, with rhomboidal faces ; if any conclusion could 

 be drawn from the two or three faces of each, which were 

 tolerably distinct. I was tempted to conjecture from a ^ew 

 imperfect measurements, that the primary form might be a 

 rhombohedron, with angles of about 124°; but this point can 

 only be decided, when we shall have an opportunity of ex- 

 amining more complete crystals. 



Fracture foliated, but rather imperfect, and no distinct 

 cleavages could be made out. 



Easily scratched by calcareous spar, but not by the nail. 



Specific gravity 3-014 to 3034 in different trials.* 



Powder flea-brown. It dissolved with effervesence in mu- 

 riatic acid, giving out some chlorine, and leaving silica. On 



* Professor Vanuxem and Dr. Troost state it to be about 4. 



