If I could hopefully add insight.

In my personal opinion and as a critique there is absolutely nothing wrong with working small. especially with a rock.

Though sometimes you do need to push yourself to bigger proportions and challenge yourself! So I advise after this to go to bigger sizes and out of your comfort zone.

@Iharoon your rock reminded me of Pokemon rocks in the Diamond,Pearl and Platinum series and in fact many of the rocks has the same width and height.



 

Look specifically at these rocks on the sprite sheet, although alot of the rocks personally in my taste are a bit dull. Shown below are rocks made by about the same pixel width and height like yours Iharoons.


I think your rock is just fine being that size however, your rock looks more like a pebble than a rock. So with my edit below I showed and added more cracks or texture to the rock to make it more like a rock and less like a pebble.



In my example I have based my palate based off your base color which uses a de-saturated red. In addition the shading is based going up the color spectrum and overall maintaining warm colors with high contrast in order to make it pop.

With sprites this small you need major hue shifts sometimes in order to make it stand out and also not make it dull. Which unfortunately your rock is and it doesn't look very lively.

However, your rock is not all that bad! its a very good attempt if its your first I can also see you understand light source so kudos to you!

I hoped this helped!