Rock.
no
Shale is a sedimentary rock that typically has the smallest grain size due to its fine-grained and compacted nature.
Sandstone is the classification of rock composed of small rounded rock particles, usually quartz in nature.
A grain can be a tiny piece of rock, yes. A grain can also be a grain of salt, meaning one 'pellet' of salt.
The smallest rock in our solar system is nothing but asteroids.
The smallest thing you could imagine - a dust grain, a molecule, an atom, a quark.
An allochem is a grain of rock in a carbonate rock.
the size of a grain of rice
Not even close.
the grain of zircon and it is the width of a human hair
Marble is has no grain so it is classified as a glassy rock.
Scientists believe that atoms are the smallest things on Earth, but they are not positive if this is entirely true. Years ago people thought a grain of and was the smallest.