698 CROSS, IDDINGS, PIRSSON, AND WASHINGTON 



Basing the comparison of the sizes of crystals on those of the 

 great number of crystals that give character to the fabric of the 

 rock, the following general distinctions may be recognized: 

 I. Equigranular rocks — composed chiefly of crystals of like orders 



of magnitude. 

 II. Inequigranular rocks — composed of crystals of different orders 

 of magnitude. 



I. Equigranular rocks. — The fabric of equigranular rocks 

 depends further on the — 



(A) Shapes of the crystals. 



(B) Arrangement or distribution of them. 



(A) Shapes of crystals may be described in general terms with 

 reference to the presence or absence of crystallographic faces as: 

 Euhedral — completely bounded by crystal faces; automorphic, 



idiomorphic. 

 Suhhedral — partly bounded by crystal faces, hypautomorphic, 



hypidiomorphic. 

 Anhedral — without crystal faces, xenomorphic, allotrimorphic. 



The crystals of equigranular rocks may be : 

 Equijorm — all the same shape, or nearly so; or 

 Multiform — having various shapes. 



With reference to their dimensions the shapes may be described as : 

 Equant — equi dimensional or nearly so. 

 Tabular — in plates or tables. 

 Prismoid — in prismatic forms. 

 Irregular — not one of the three preceding divisions. 



More specifically crystals may be described further under each 

 of the general shapes just named, as follows: 



Equant. — Cuboidal, polyhedral, spheroidal, equant anhedral, 

 equant subhedral. — The simplest examples of equant^ equijorm, 

 equigranular^ fabric are found in an evenly granular quartz vein, 

 in some quartzites and crystalHne limestones, and in certain anor- 

 thosites, dunites, and pyroxenites. 



Tabular. — Tabular, platy, foliated. The crystals may be in 

 plates, tables, disks, folia, scales. — The best examples of tabular, 

 equiform, equigranular fabric are found in certain feldspar rocks: 

 syenite with so-called trachytic fabric, hedrumite, and certain anor- 



