PHYSIOGRAPHY. 45 



Mica Microlite. 



ix. Hemidomatic Rock-Mica. BREITHAUPT. 



Primary form. Oblique rhombic prism. M on M =3= 118. 



Cleavage, parallel with M, perfect ; with the shorter diagonal, 

 in traces. 



Lustre metallic pearly. Color grey and brown. Optical axis 

 double. Streak greyish white. 



Flexible in thin laminae. Hardness (scale of BREITHAUPT) 

 = 2-0. Sp. gr. = 2 956 . . . 2-983. 

 1. The present species is cited from Zinnwald, Bohemia. 



x. Siderose Rock-Mica. BREITHAUPT. 



Primary form. Oblique rhombic prism. 



Cleavage, perfect parallel with M. 



Lustre pearly. Color dark green to black. Optical axis double. 

 Streak green to greenish grey. 



Slightly flexible in thin laminae. Hardness (scale of BREI- 

 THAUPT) = 3-25 . . . 3 50. Sp. gr. = 3-146 . . . 3-190. 



1. Locality, Altenberg, Saxony. 



x. Rhombohedral Chrysophane-Mica. BREITHAUPT. 



Primary form. Acute rhomboid. 



Cleavage, the same as in Tautokline Aster-Mica. 



Lustre metallic pearly. Color yellowish brown to pinch-beck 

 brown. Optical axis single. Streak yellowish grey, almost pale. 



Scarcely flexible in thin laminse. Hardness (scale of BREI- 

 THAUPT) = 5-0 ... 5-50. Sp. gr. = 3-071. 



1. This mineral is said by BREITHAUPT, to have been sent to Europe 

 from the United States, under the name of Clintonite, and to be found at 

 Warwick, (N.Y.) Its locality is more probably Amity; and it appears 

 to be the variety of Bronzite, described page 89, vol. i. of this work. 



MICROLITE. Octahedral Tungstic-Baryte. 

 Primary form. Regular octahedron. 



