A. J. Moses — Crystallization of Molybdenite. 363 



lated angles are 55° 45' and 65° 35'. Relatively they are 

 fairly close to calculated angles, for a unit angle of 64° 27' 

 would require for (2023) an angle of 54° 21'. It is not 

 unreasonable to suppose an error in orientation or in the read- 

 ing of the faint prismatic signals which would diminish both 

 angles about the same amount. 



The conclusion, therefore, is a dominant pyramid (2023) 

 with striations due to an oscillation between this and (1011) ; 

 the prism (1010) present as a slightly developed modification. 



7. The Knop and Homes Measurements. 



The crystals from Auerbach, Hesse, examined by Knop,* were 

 parallel plates often with curved lamellae. No regular twin 

 striations but frequent wrinkling which appeared to be perpen- 

 dicular to the sides of the hexagon producing approximations 

 to rhombic thirds of faces. Measurements did not give any 

 constant angles between these ' thirds,' which were evidently 

 results of bending or wrinkling. 



Although, as might be expected, these bent crystals gave no 

 constant angles,f it is noteworthy that the averages both of the 

 angles with the cleavage and the angles between adjacent faces 

 closely approach those of the unit pyramid. 



Faces with cleavage. 

 71° 0' 

 69 04 

 57 20 





Adjacent faces 







50 c 



07' 







56 



49 





age 



56 



37 



Avei 



54 c 



*».!/ 



65° 48' 



The Frankford, Pa., unit pyramid (1011) has angles respec- 

 tively 54° 10' and 65° 35'. 



With respect to the crystals from Greenland, Homes states : 

 " I have measured the crystals from Narksak and found the pyra- 

 mid 1 23° 45', 140° 57 / .";j: Kenngott reexamined§ the crystals 

 and accepted the proof of their hexagonal form but pronounced 

 the pyramid dubious, attributing it to the slipping of curved 

 prisms and to tapering, but states, " one small crystal only 

 showed a fairly distinct acute hexagonal pyramid." 



Hintze| gives these angles as^><? =70° 28 J-' and^> =56° 15'. 

 There appears to have been a slight error here, as for jop = 

 56° 15', pc = 70° 31J'. This corresponds to (5054), for which 

 the calculated angle is 70° 03'. 



* Summarized from Neues Jahrb. f. Min., 1848, p. 43. 



f Obtained by attaching mica to the faces. 



I Uebersicht Darstell. des Mohsischen Min. Syst., 1847, p. 115. 



§Min. Forschungen, 1856. p. 104. | Mineralogie, vol. i, p. 104. 



