I18RARY 
OF THE 
iJMIVERST'oMl'.'ilOiS. 
THE 
AMERICAN GEOLOGIST. 
Vol. XXI. APRIL, 1898. No. 4 
AN OCCURRENCE OF ACID PEGMATYTE 
IN DIABASE. 
By T. A. Jag(j.\e, Jr., CambridKe, Wass. 
(Plate XIV.) 
The presence of quartz and acid feldspar in diabase, as 
primary constituents, has been frequentl)- described,* and the 
primary nature of the minerals is said to be demonstrated by 
granophyric intergrowths of quartz with feldspar,t and by the 
occurrence of quartz in idiomorphic phenocrysts.? Torne- 
l^ohm's Swedish type§ is described as containing, in the inter- 
spaces of the plagioclose laths, an intergrowth like graphic gran- 
ite, consisting of parallel groups of quartz needles in colorless 
feldspar. Rosenbusch|| has mentioned the remarkable abund- 
ance of this so-called Konga type of diabase, occurring in many 
parts of the world, characterized invariably by "quartz-feld- 
spar aggregates in most delicate granophyric intergrowth, 
such as is observed elsew'here only in granite-porphyry and 
quartz-porphyry." Rosenbusch states, however, that the dis- 
crimination of primary and secondary quartz is very difficult, 
and that, in diabase, it is more frequently secondary.' 
*Zirkel, Lehrbach der Petrographie, 1894, p. 631. 
tRosenbusch, Mikros. Physiographic, 1896, vol. II, p. mi. 
Zirkel, loc, cit. 
Harker, Petrology for Students, 1895, pp. 109- no. 
J Zirkel, loc. cit. 
§ N. Jahrb. f. Min„ 1887, p. 258. 
II Op. cit, p. 1 144. 
