We have 3 types of samples up until now in MCO: Ground samples, Core samples and Rock samples.
Ground samples are picked-up by a player simply by hand. They look like this:
(http://img844.imageshack.us/img844/9727/dirtbag.png)
The thing is - the core and the ground sample icons look the same.
Every core sample I have ever seen looked like this:
(http://media.knoxnews.com/media/img/photos/2010/08/02/080210volunteer12.mc_t607.jpg)
As you can see - the core samples are long rod-like. That's becouse they are taken from a drill sampler.
The difference is only graphical, but firstly: it's more real that way, and secondly: it make's easier to distinguish different sample types.
For that matter, it would also be cool and practical if rock samples would look like they are a part of a bigger rock.
(http://www.landscapesupply.ca/products/attachments/WRP_red.png)