Reactive Crystals are what you might have already seen while completing the Heart of Deimos quest, they were used as a puzzle to unlock a door. These crystals are spread across the infested open-world of Deimos. I was confused at first, about what they actually do, but there’s always something to do with the operator in every update.
There are multiple of these in tunnels and vaults where you might have to go to complete certain bounties. This is really useful if you are soloing the content, the crystals also have a short cooldown so they can be really useful in time of combat.
You will come across them while running around in Deimos or while completing quests for the Mother. To complete the puzzle switch to Operator mode, you have to match the shown symbols and shoot them accordingly. After doing that, you will be granted some sort of buff; this can be enemies fighting for you or form a shield wall that stops enemies from reaching you.
These are the only things that I’ve found so far while trying to interact with the Reactive Crystal. There might be more to it, but so far this isn’t connected with anything that is required to be completed for any quest or bounties other than the mother ones.