KOlllg.] 510 JJ(1„ ,g^ 



a is a cleavage face and reflects a sharp image, the other faces are true 

 crystal faces, ami, with the exception of c, reflect very imperfectly. The 

 largest face (a) is not quite one-eighth of an inch wide. The measurement 

 does not make any pretension of scientific accuracy for the reasons stated, 

 yet the above angles are the means of repeated observations, which only 

 difTcred by 1° for the edges a /\ e, c ,\ e, and by less tlian 3U' for the 

 other edges. Their approximate accuracy taken for granted, they clearly 

 admit only an interpretation according to the laws of the monosymetric 

 system, when c becomes the basal plane, e an orthopinakoid, band d hemi- 

 domes. 



Scheerer, who first described the species (B. H. Ztg. XIII 240, 1854) ar- 

 rived at a different result. His measurements lead to an orthorhombic inter- 

 pretation, and the optical investigations of Des Cloizeau (Dana, mineralogy) 

 corroborate his view. But as none of the angles measured by me, find and 

 analogon in those given by Scheerer, no comparison can be made, and future 

 study must decide the truth. 



Structural properties. A very marked cleavage exists parallel lo the face 

 c, by which the structure becomes eminently micaceous. Tlie cleavage is 

 indicated on tlie lateral faces by a decided striation (very plainly visiljle on 

 the quartz, after tlie removal of crystals), and re-entering angles. Unlike 

 other micaceous minerals, the laminiB are but very slightly elastic and te- 

 nacious, being easily reduced to a fine powder. That the crystals break 

 easily across the main extension has already been mentioned. Hardness 

 about 3. 



Optical properties. Color from brass yellow to deep bronze brown. 

 Transmitted light deep yellow to reddish brown. Appearance of the 

 powder at a certain degree of fineness like mosaic gold. I could not obtain 

 an image of interference with a lamina, through which t3'pes of ordinary 

 print were plainly visible But not possessing much experience in optical 

 investigation, I liave referred it to Professor P. Groth, of Strassburg. 



Specific gravity = 3.375 at 15 0°. 



Pyrognostic properties. The mineral fuses xety readily to a black 

 globule in the flame of an oil lamp. With microcosmic salt the reactions 

 for iron, manganese, titanium and silica are easily obtained. 



The mineral decomposes completely with sulphuric acid at ordinary 

 pressure, and very readily in a sealed tube at 140 C^. 



24.363 

 2.294 



