What you have encountered is a shiny Geodude, which, as you described, is gold and a normal Geodude is a light gray color. Think of shiny Geodude as a gold nugget and a normal Geodude has a regular rock.
A female Geodude can be found randomly in the wild. A Geodude has a 50% chance of being female.
Anywhere you can find normal Geodude. Shinies are randomly generated and very rare. The chance of finding one is less than 0.001%.
No, Geodude is not known to be found in the water areas in Pokemon Diamond, Pearl, and Platinum, unless it was cheated with a cheating device.
They are able to be found is many of the outside routes but *for sure* in any cave in the game!
Zubat, Paras, Clefairy, Jigglypuff, Geodude.
Geodude. graveler, nosepass, shuckle.........
Zubat (Many) Geodude (Many) Paras (Some) Clefairy (Few)
where ever you find geodudes one could be shiny i found a shiny before my first gym it was in Oreburgh Gate on Pearl
you can get them by some ways,they are in caves,u can mate some of their evolutions[gravler is found on victory road] and the rocks to the north of marville that u use rocksmash on can be brokken and a geodude might be in it, if they aren't in either rocks just go running around in some caves
there are cubone, geodude, and a lot more that i don't know about. I'll get back on that later
Explosion is not a tm so cannot be found anywhere. However a variety of Pokemon learn Explosion naturally such as Koffing, Geodude and Voltorb.
I found my Geodude in the Safari Zone. I am pretty sure you can also catch them in all of the caves, but I may be wrong. To get Geodude in the Safari Zone you walk into the Safari Zone Building and talk to Baboa. He'll talk to you about a challenge, in this challenge he'll ask you to catch a geodude. He'll tell you where they are, just search around a while and you'll find one. Have a good amount of Safari Balls left because I had to go in again because when I found one I ran out of balls before I caught it. Hope this helps.