You have identified your rock as having a crystaline structure.
You have told us your sample has a random crystaline structure: This means your rock is an igneous rock.
You have reported your sample has a crystal structure of medium-sized granules.
Is this correct? If not, start again or go back a step.
Thinking now about the colour of your rock:
If the colour is light, we have identified your sample as microgranite
If the rock is of an intermediate colour, we believe your rock to be microdiorite
If your sample is dark, we can identify your rock as micrograbbo
More help with this question:
Rocks come in a multitude of colours, for simplicity we have divided them into three catgories:
Dark coloured rocks: may be black, dark brown, dark grey or dark green.
Intermediate coloured rocks: are pale grey, reddish brown or green.
Light coloured rocks: are pale pink, pale green, light grey or white.
Tip: the colour of a rock can also be influenced by its grain size. Very fine grained rocks often appear much darker than their coarse grained or coarsely crystalline equivalents.