I did one for Fire and Hack, so the last one left is Heinrichite (on his creation day too!). So here's some lore about this boy:
Like Fire, Heinrichite's gem code pays homage to the day he was created. His code is Facet 3 Cut 3MO (or 3/30 (O substituting for 0) with the M representing March)
Heinrichite has thermokinesis. It helps him keep his gemstone cool and avoid dehydration. This is important because the water inside his gemstone seals the radiation it produces.
He also has a sealant for an extra layer of protection in case his gemstone cracks.
Created for Pink Diamond's first colony, he was placed on a moon station where Gem invaders came to refuel their ships. Because it was so small, he was the only sentry there (depending on how big the facility is, there can be up to four heinrichites guarding a place)
Heinrich was originally a lot like the others of his kind: territorial and a lone wolf who took his job seriously. But during the long and boring days with no visitors, the Prasiolites would come up to his tower to hang out with him. Moss Agate, the Gem who ran the station, would come to collect them. Eventually, she also started getting chummy with him. It was because of them that Heinrich became more inclined to be with other Gems.
His Quartz friends were eventually drafted to fight the Gem War and he waited for them, but they never returned. He would wait over 3,000 years in his lonely station until Hack finds him.
Heinrich is incredibly sturdy: it takes a lot to poof him, even if he was stabbed. He is also capable of keeping his form together for a long amount of time before he eventually poofs.
He has mixed feelings about Earth. It's where his friends were sent to and corrupted and a part of him resents the planet for it. But on the other hand, it's full of beauty and wonder. Visiting Earth actually helped him come to terms with his past.
Heinrichite's gem is relatively huge and takes over a good portion of his upper head, even overlapping on one of his eyes.
His visor has a lot of cool features. Not only can it upload maps and see Gems through structures (Gems show up as silhouettes made of light), but he also has a 360 degree visual mode where he can see from all directions. The only downside is that he can't walk while using most of the features as it will constantly try to recalibrate, causing nausea and dizziness.
Eventually, Heinrichite's thermokinesis upgrades to hydrokinesis. He's able to create and control water, ice, and steam.
One of his biggest weaknesses is putting others before himself. It's a leftover of his instinct of being a sentry: needing to protect something. So he often throws himself in front of Hack or Fire, no matter how scared he is. He almost got shattered a couple of times doing this.
He often feels like a third wheel to Fire and Hack. He admires them a lot, but feels he's inadequate when compared to them. His feelings are sometimes reinforced by other Gems they come across on their journey together.
