Grain shape.
texture
texture
The texture thus described is referred to as aphanitic texture.
The rock with the finest grain size is typically shale. Shale is a sedimentary rock composed of clay particles that are less than 1/256 millimeter in diameter, giving it a very fine texture. This fine grain size allows shale to split easily into thin layers, which is a characteristic feature of the rock.
fined grain texture
Grain
Grain
Grain shape.
texture
Because of the gravity ..
It doesn't. The grain size effects the texture. If a rock has a small grain size, it will have a smooth texture. If the grain size is large, such as pebbles, the texture will be rough. For example, siltstone is one of the smoothest rocks because it contains silt particles, which are .0004cm to .006cm. Conglomerate though contains various particles including cobbles and boulders, which are from 10cm to 100cm.
Because of the gravity ..
These characteristics determine a rock's texture.
texture
Large crystals with a coarse crystal grain texture.
The size of the grains in a sedimentary rock can be determined by examining the texture of the rock. Coarser grains indicate a larger grain size, while finer grains indicate a smaller grain size. Other features that can provide clues to grain size include the sorting (uniformity of grain sizes) and rounding of the grains.