ART. 28 MINERALOGY OF TRIASSIC LIMESTONE SHANNON 25 



Measurements of datoUte crystal, Figure 5 



Quality description 



Ex. 2 signals 



Good 



V.g 



V.g 



Uniformly dull.. 



Excellent 



Deeply corroded 

 Rounded, fair... 



V.g 



Dull, etched 



V. p. dull 



Excellent 



Medium 



Med., wavy 



Excellent 



Etched dull 



Fair 



Measured 



89 37 



90 00 

 57 54 

 38 50 

 N.s. 



30 

 N.s. 

 90 00 



56 25 

 38 12 

 38 14 

 21 12 

 47 37 



57 02 

 67 20 

 57 02 

 72 44 



00 

 90 00 

 90 00 

 90 00 

 N.s. 

 32 31 

 N.s. 

 18 32 

 21 23 

 67 52 

 39 34 

 53 54 

 28 57 

 49 41 

 58 23 

 64 01 

 78 34 



Calculated 



90 00 

 90 00 

 57 37 

 38 14 

 07 

 14 

 90 00 

 90 00 

 57 48 

 38 19 

 38 23 

 21 36 

 46 26 

 57 33 

 67 03 

 57 34 

 72 25 



00 

 90 00 

 90 00 

 90 00 

 51 41 

 32 19 

 45 00 

 18 31 

 21 36 

 58 12 

 38 55 

 53 43 

 28 51 

 49 42 

 57 49 

 67 03 

 76 34 



The faces of m^ (Oil), Q 

 (122) Y (124), and n (TTl) 

 are etched uniformly dull 

 while X (102) is not merely 

 dull but is deepl}^ pitted and 

 corroded, s (112) and Y 

 (334) are ribbed and striated 

 parallel to their mutual inter- 

 section, a peculiarity since 

 such striations on e (Tl2). 

 almost invariably present on 

 the crystals of this mineral 

 fro m other localities, are 

 usually parallel to its inter- 

 section with m (110). 



A small face, not shown 

 on the drawing, which oc- 

 curs between Z (116) and y 

 (124) gives angles indicating 

 a new form with the indices 

 (2.3.10) . The negative pyra- 

 mid u (211), recorded as a 

 new form on datolite from 

 Westfield, Mass., is here con- 

 firmed. 



There is an alternate position possible for these crystals whereby 

 the broad face indicated as c (001) in the drawing becomes a (100) 

 and the sm'all triangular face, above made a (100) becomes c (001), 



Fig. 5. — Datolite. Crystal from a specimen 

 on which all the crystals, like the one 

 figoredj are different fro.m the prevailing 

 habit at the locality. shows several 

 dnusoal forms 



