Mission 8 part 2, WTF?

I'm stuck on mission 8 part 2. Collecting gems? I see them on the ground, a little arrow points at it but I can't pick it up & my squad does nothing but kill things till I run out of health. WTF! Any answers to help me past this before I erase this from my hard drive. I play videogames to relax & so far this is causing nothing but anger & frustration.
If this is a joke I'm not laughing anymore!

you have to take the gem (weapon) by switching your weapon.

Ahh, thx. This game needs a manual!