The American Naturalist. 



MINERALOGY AND PETROGRAPHY. 1 



Quartz and Feldspar Inclusions in Diabase.— Backstrom 2 has 

 discovered in several Scandinavian diabases inclusions of quartz and feld- 

 spar, and has carefully studied the effects produced by the reactions 

 between them and the enclosing rock magma. The diabase consists of 

 labradorite, three augites, magnetite and several secondary substances, 

 and has a structure that differs slightly from the diabasic structure, in 

 that the angles between the plagioclase and the more or less columnar 

 augite, are filled with a groundmass of feldspar laths, pyroxene 

 needles, magnetite and chlorite. Near the quartz inclusions the quan- 

 tity of the groundmass increases and the diabasic structure becomes 

 obscure, until it finally disappears, and in its place is seen a porphy- 

 ritic aggregate with thick tabular crystals of plagioclase, well formed 

 augite prisms and large grains of magnetite in a groundmass that 

 occupies a third or a half of the field of view. Very near the quartz 

 the plagioclase become smaller, and spherulites of quartz and feld- 

 spar more abundant, of which the latter mineral is either orthoclase 

 or oligoclase. The feldspathic inclusions in the rock are orthoclase, 

 microline and plagioclase. The action of the magma upon the micro- 

 line is shown in the existence in it of ' solution-spaces, ' which are 

 spaces dissolved from the midst of the mineral and afterwards filled 

 with rock magma, from which have crystallized pyrite, magnetite, 

 ilmenite, needles of pyroxene, lath-shaped crystals of oligoclase, grains 

 of quartz, calcite and masses of chlorite. The orthoclase inclusions 

 sometimes become granulated, or filled with long lenticular areas of a 

 feldspar whose origin is the same as that of the minerals in the solu- 

 tion spaces. Plagioclase fragments have also undergone granulation, 

 and the new feldspar has crossed the original twinning planes irre- 

 spective of their directions. Other fragments are more completely 

 penetrated by the magma, so that everywhere throughout their mass 

 may be detected small areas of the diabasic groundmass with its 

 spherulites. The peripheries of the grains are often marked by 

 growths of new, colorless, transparent plagioclase, crystallographically 

 continuous with the enclosed mineral. Mica, hornblende and other 

 iron-bearing compounds seem less capable of resisting the action of the 



^Edited by Dr. W. S. Bayley, Colby University, Wa.erville, Me. 



'Bihang t. k. Svensk. Vet. Akad. Handl., B. 16, Afd. II. No. 1. 



