|
Texture: |
Desirable |
Potentially Objectionable. |
|
Crystallinity |
Crystalline |
Partially or entirely glassy |
|
Grain size |
Medium to fine grained |
Very fine grained, Aphanitic, pegmatitic |
|
Intergranular bond |
Interlocked, good bond |
Poor bond, coarse grained minerals with perfect cleavage |
|
Packing of grains |
Dense |
Loose |
|
Granularity |
Medium to fine grained |
Aphanitic, conglomeratic |
|
Cementation |
Well cemented |
Poorly cemented, porous |
Crystallinity in this case applies to igneous rocks and their rate of cooling. Slow rates result in coarser crystals, whereas fast cooling results in a volcanic glass.
Grain size and grain sorting (gradation) determines pore size; the very fine grained rocks have many small pores. Coarse grained rocks may have larger pores if the grain size is uniform. Well graded (combination of grain sizes) rocks may have small pores.
