Doesn't look like anyone is having luck with your pill. The closest I could find is "E177. The stylized E is often mistaken for a G. The color is a match but I think you said it was round, not oblong.... I know it's doubtful but I hate to see a thread with 0 replies :/
Okay, I'm 99% positive your son's tablet is sennosides, an OTC laxative. It's generic for Senokot.
I have three different store brands. All three are blue coated and shaped like an M&M candy or an Advil tablet. All three are about 10 mm in diameter and about 5 mm thick.
I cut open one and it does have a very thin layer of white. So it's a robins egg blue on the outside, a thin layer of white under (or part of) the coating, and the interior of the pill is brown. In fact, your 'sawdust' description is a perfect description of the color and texture! Thanks so much.
I don't know the manufacturer of the G 177 tab. It could be Granutec or possibly Guardian.
Granutec uses a plain uppercase "G" and Guardian uses a stylized "G". Check out Guardian's website and take a look at the "G" logo in the upper left corner of the home page:
Thank you so much! Laxatives are the least of my concern with him. I am so relieved to know that is all it is. He has some problems that I am addressing and I was worried this was yet another pill. Thank you so much for your help!