The term texture as used here refers to the smaller features of ores which are dependent on the size, forms, and arrangement of the component minerals and in some cases upon such features as mineral cleavage, mineral parting, mineral contacts, and minor fracturing. These features can be observed in hand specimens either with the unaided eye or with the microscope. For those larger features of ore deposits that are dependent upon folding, faulting, jointing, bedding, etc., the term structure is applied. Since the distinction between texture and structure is in important part one of size, the writer reserves some latitude in the descriptions. This usage of the terms texture and structure conforms to that commonly adopted by petrographers, and this is desirable since ores are merely unusual rock types.
Some textural terms well established among petrographers, are also appropriately applicable to ore textures and have been widely used in ore descriptions. Petrographic terms used in describing the shapes of crystals are:
Idiomorphic or euhedral if the crystal contours are more or less perfectly developed.
Xenomorphic or anhedral if crystal contours are not developed.
Hypidiomorphic or subhedral if crystal contours are partially developed.
In all interpretations of ore textures it is important that the texture be visualized in three dimensions, although a single thin section or polished section displays only two dimensions. In magmatic ores of granular texture it is usually safe to assume that the third dimension is similar to the other two, but in magmatic ores showing either graphic . . .