124 Prof. W. H. Miller on Quartz, Ice, and Karstenite. 



50 19 19, notwithstanding the lower values of the indices of the 

 former symbol. 



Ice. 



In a memoir by Franz Ley dolt, entitled " Beitrage zur Kennt- 

 niss der Krystallform und der Bildungsart des Eises," it is 

 asserted that ice has no cleavage (Sitzungsberichte der mathem.- 

 naturw. CI. der kais. Akad der Wissensch. Band vii. Abth. 2, 

 p. 477). A good many years previously I had seen some plates 

 of ice broken which exhibited a separation parallel to the sur- 

 faces of the ice so perfectly like cleavage, that I never hesitated 

 to publish the statement that ice has a cleavage parallel to the 

 faces of the form 111. A considerable time elapsed after the 

 appearance of Leydolt's paper before an opportunity of making 

 further observations presented itself. When at last I obtained 

 some thick plates of newly formed ice, I was unable to procure 

 a trace of cleavage by the application of knife, chisel, or point 

 in a direction parallel to their bounding planes. On throwing 

 one of the plates on the hard frozen ground it broke across, ex- 

 hibiting in the fracture two planes normal to the natural faces 

 of the plate, and apparently (for I had not at hand the means of 

 measuring the angle they made with one onother) parallel to two 

 adjacent faces of a regular six-sided prism, looking like very per- 

 fect cleavages, and affording by reflection distinct images of sur- 

 rounding objects ; but I was unable to obtain a trace of clea- 

 vage in planes parallel to either of those revealed by fracture. 

 It is therefore obvious that the separations, as well parallel as 

 normal to the surfaces of the plates of ice, were due to the exist- 

 ence of faces of union and not to true cleavage. The latter planes 

 are probably those of the six-sided prism 101; for some crys- 

 tals of ice examined by A. E. Nordenskjold were combinations 

 of the simple forms 1 1 1, * 32 1, k2 1 0, /c5 1 3, 1 I. The 

 angles which normals to the faces of these forms make with a 

 normal to 1 1 1 are approximately : — 



111, 321=38° 57'; 111, 210 = 58° 15'; 

 111, 5 13 = 81° 31'; 11 J, 10 1 = 90°. 

 (PoggendorfFs Annalen, vol. cxiv. p. 612.) 



Karstenite. 



A small cavity in the interior of a mass of Karstenite (CaO SO 3 ) 

 from Luneburg was found to be traversed by several slender 

 crystals attached at both ends to the walls of the cavity. These 

 crystals exhibit some simple forms hitherto un described, and 

 several of the forms first observed by Hessenberg and described 

 by him in the 10th Number of his " Mineralogische Notizen," 



