It is in the top right section of the lunar map, just up from the main Moon base.
To enter the Rock lab, you need a keycard (dropped by Salerno when you find her) and purple eyes that you can get from the machine in the Research Lab.
The entrance is at the left side of the main base. There are entrances at the bottom of the Research Lab, at the bottom of the BioDome, and at the left side of the Rock lab.
You need purple eyes to pass the retina scan at the Rock Lab. As explained on the computer in the Research lab, it can fool the scans used for security. Change them in the Research Lab. They will change back automatically.
There are two: - the BioDome is the second place you travel to in the rover. - the circular Infirmary is part of the Research Lab, the first place you go.
There is no electric saw on Lunar Colony. To enter the Infirmary at the Research Lab, climb to the top and use the pressure chamber to temporarily squash you down, then quickly slip past the boxes that are blocking the door. The exit from the Infirmary is in the maintenance area.
The yellow artifact (gem tower) is just above the Research Lab in the upper right of the lunar map. However, there is no value in going to it. The Red artifact is below the BioDome, and the Green artifact is just below the main lunar base.
There is an eye-color changing device just inside the Research Lab (north of the main base). Change yours temporarily to purple to fool the retina scan devices.
You get the keycard when you follow Salerno to the BioDome. As she escapes, she drops the card by the airlock. You will chase her in the rover to the Rock lab, but you also have to have purple eyes to fool the retina scan. You get them when you are at the Research Lab (upper right by the airlock). To find Salerno, you have to get the tracking device from the Infirmary.
It is in the Research Lab north of the main moon base. Drive there, move the meteor with your winch, and enter. The pressure chamber is at the upper left of the main room. You can squash yourself flat (temporarily) to squeeze past the blocks into the Infirmary.
On Lunar Colony, you use the lunar rover to reach the 3 outlying centers of the lunar base: the Research Lab, the BioDome, and the Rock Lab. You are trying to locate Commander Salerno, who is investigating the mysterious artifacts on the lunar surface. To charge the rover in the Vehicle bay, climb up to the top right and open the sun shade. Tilt the reflector dishes to aim the sunlight at the solar panel on the rover (each one reflects onto another reflector). Get the Gatos Manual from the open locker and go to the barracks. Use the computer on the 4th level -- the reboot code in the manual is square-loop-circle-x. Use the slider at the left to unlock the airlock door. Now you can use the rover to reach your first stop, the Research Lab a little ways up from the main base.
Just as you enter the Research Lab (building north of the main base), you will see the eye-color research unit. It states that purple eyes may cause detection problems with retina scans. Change yours to purple (they will change back when you finish the quest).
The Purple Artifact is actually just slightly below the Rock lab on the map and can be seen as a faint purple glow. But you cannot do anything with it until you have the Geiger Counter from the Rock Lab.