434 Prof. Maskelyne and Dr. Lang's Miner -alogical Notes. 



Fig. 2.— 110, T03, 101 



1 03 (I 00) 1 03 = 16° 24'-40' (16° 38'). 

 Fig. 3.— 110, 104, 124 



104 (100) I 04 = 11 40 (11 46) 

 124.124=22 30 (23 46) 

 104.101 = 34 26 (34 45) 

 Fig. 4.— 110.124.101 



I 3 4.1 3 4=34 appr. (35° 2')- 



After the engravings of Plate VI. were done, I found on a 

 specimen of melaconite from Joachim sthal 

 in Bohemia small crystals of malachite show- 

 ing only the forms 1 1 0, 1 0, 1 0, 1 1, 

 but remarkable for the unusual predomi- 

 nance of the plane ] 0, as is represented 

 in the accompanying woodcut. On some of 

 the crystals the prism planes were not to be 

 found at all. 



The second type of crystallization was found 

 on specimens which came from the same 

 locality in Australia, the malachite coating 

 the sandstone in a uniform layer. The crystals are shortened in 

 the direction of the axis of the zone of the prism 10 0; they 

 adhere to the stone by their posterior part, and seem to occur 

 sometimes also not twinned like fig. 6, which is a combination 

 of 110. 100. 010.13 4. I found on such a crystal 



1 3 4 . 1 3 4= 34 42 (35 2 calc) 

 13 4.110= 83 30 (83 25 „ ) 

 134.1 I = 106 ap. (105 26 „ ) 



But other crystals, as in fig. 7, are twinned, the two individuals 

 penetrating each other in the same manner as described before. 

 The prism-planes of the two individuals are very seldom in one 

 plane, but form reentering angles of from to 7 degrees. The 

 crystal fig. 6, a section of which parallel to the plane of sym- 

 metry is given in fig. 8, is a combination of 1 1 and 124, and 

 yielded the angle 



1 2 4 . 1 2 4=23° 22' (23° 46'). 



In this group, however, the planes 12 4, 13 4, 1 4 are stri- 

 ated parallel to their mutual intersection, and therefore cannot be 

 measured with accuracy. 



With regard to the optical properties of malachite I have the 



