TEXTURE OF IGNEOUS ROCKS 699 



thosites. It will be found in some micaceous metamorphic rocks 

 with highly developed foliated texture. 



Prismoid. — Parallelopipedons, lath-shaped blades, prisms, spin- 

 dles, fibers. — Examples of prismoid, equiform, equigranular, fabric are 

 rare among igneous rocks. The most familiar examples are certain 

 metamorphic, actinolite rocks : strahlstein. 



The great majority of equigranular rocks are multiform, since 

 they consist of several kinds of minerals whose characteristic shapes 

 are not alike. Quartz is almost always equant, micas are nearly always 

 tabular, amphiboles frequently prismoid ; whereas feldspars may be 

 equant, tabular, or prismoid, and pyroxenes may be equant or pris- 

 moid. The various combinations of these shapes produce fabrics 

 which have no simple character and require specific description. 

 They frequently recur and should be distinguished by simple terms 

 for convenience. 



(B) Arrangement or distribution of crystals in equigranular 

 rocks produces differences of fabric, 



1. Equant. — Where crystals are equant there can be no varia- 

 bihty in the arrangement which would affect the fabric, so far as 

 form alone is concerned. But in case there are more than one kind 

 of mineral present, especially if they are of different colors, the dis- 

 tribution of equant crystals of different kinds produces variations 

 in fabric as regards color — varieties of color pattern. 



2. Tabular. — The tabular crystals may be arranged in the follow- 

 ing ways: 



Parallel. 



Subparallel. 



Diverse, in all directions (omniversal). 



Radial, divergent, fan-like, spheruKtic, concentric, imbricated. 



3. Prismoid. — The prismoid crystals may lie in the following 

 positions : 



Parallel. 

 Subparallel. 



Diverse, in all directions (omniversal). 

 Radial, divergent, spherulitic, axiolitic. 

 Tangential, around a nuclear crystal. 

 . 4. Irregular. — Crystals of irregular shapes forming equiform, 



