i made this rock in a 32 by 32 canvas; any shading criticism is welcome
I think that small rock needs little shading wisdom. The only thing I can say is that this little rock’s lights to shadow colors must be able to stand out if you squint(Make the rock a recognizable shape), and mid-tones-(the two center grey colors) are maybe too close together in the light spectrum. Other than that, you have options for what you COULD do, such as outlines(make sure to vary their colors with colors other than black). You can also look at pictures of rocks and try to create similar shapes and colors. As well you can decide which direction you want your light to come from if that would be fun.
Here is a quick but also small, rock sprite.