Kraus and Cook — Datolite from Westfeld, Mass. 23 



development, which may be characterized as the pyramidal 

 habit. The following. forms were observed on this type : 



a{100}, ft{010},c{001},m{110}',r{230},o{120{,?{I30},aj'{102|, 

 v{103}, w|l04{-, m^jOll}, #{012}, £{013}, m y {067} (new), 

 m^JO'l'lO} (new), n {111}, (3 |121|, Q fl22}, vjlll}, b {223}, 

 €{112}, A{113}, /x{114}, #c|lJ5},w g {l*l-10} (new), M{122}, »jl23}, 

 a{124}, tt{231}, e'{148}, // {1'4'10}. 



The pinacoid a {010} is always present as a brilliant face. 

 The form o { 010 } occurs on about fifty per cent of the crys- 

 tals of this type. "When present, it appears as a narrow edge 

 giving good reflections, c {001} is generally very small, often 

 giving no image whatever. The prism m{110} is usually to 

 be observed as a thin edge and is always present, o { 120 } , which 

 is frequently present, possesses two characteristic outlines (figs. 

 1 and 4). In some instances it shows natural etching. It then 

 appears as a very dull face giving poor reflections. ^{230} 

 (fig. 2) was noted on several crystals, giving very good readings. 

 £{130} was observed on but one crystal, beveling the edge 

 between the faces "(111) and m^Oll). 



2 3 



The negative hemi-orthodome ${102} is the predominating 

 form of this type and aids materially in orientating the 

 crystals. The faces are often broken and the surfaces are more 

 or less uneven, and hence give poor reflections. ^{103} and 

 ^{104} were observed but once as very small, narrow edges. 

 Of the clino-domes ^{011}, ^{012}, and £{113} are always 

 present. Of these forms, m x {011} is always large. m y {067\ 

 (fig. 3) and m s {0"l*10} are new to datolite. Even though they 

 were observed on only two crystals, the observed and 

 calculated angles, nevertheless, leave no doubt as to their 

 identity. 



Observed. Calculated. 



1)1. 



= (067) : (067) 94° 39' 



= (0-1-10) : (0-1-10) 14 38 



Of the pyramids, n{lll\, /3{121 



,,{111}, 6- 



94° 46' 

 14 25 



112k M113 



ft {114} are generally present, — "{111} usually predominating. 



