Poor old Petra Kristensen. When your tenure on the X-Men is brief enough to make Changeling look like a mainstay of the team, it's probably time to write your acceptance speech for the Most Inconsequential Xaverite Ever award (though I guess she'd tie with Sway, but that's another post). Like Changeling, we only even learned Petra was on the team some time after she'd bought the farm , though at least Kevin's death was revealed fairly quickly after the event. It was decades after her spit-and-cough that we were told the truth, that there once was a super-hero called Petra who died like a bitch halfway through her first mission . Plus, sacrificing one's life to save the world from a subterranean tyrant? Reasonably awesome. Getting set on fire by a mad island? Lame.
It feels like I say this almost every time, but writing a piece on Petra is particularly difficult. She appears in all of three issues of Deadly Genesis, aside from an occasionally glimpsed psychic echo. In total, she appears on sixteen pages, and has roughly that many lines, none of which actually reveal anything about her other than she wants to join the X-Men, enjoys her training, and doesn't like her pies being stolen (and who does, right?). Not much to go on, really.
Complicating this is the fact that what little is known about her past from various sources includes information that I can't actually trace to any given comic book. All Deadly Genesis offers is the following: she is a runaway who has spent years honing her power before MacTaggert discovers her. The power in question is the ability to control rock and earth. Obviously, this allows for all sorts of earthquake/tidal-waves-of-rock hi-jinks to ensue, but there are potentially more practical applications, too. As Moira herself says, "I once saw [Petra] turn a piece o' rock coal into a diamond."
Think about that for a second. Petra holds the ability to make herself pretty much as rich as she damn well pleases. I'm not an expert on scarcity or economics or even stuff what is shiny, but I'm guessing that she could make enough money to make herself Queen of Wherever She Wants without generating so many diamonds she floods the market. The fact that she instead becomes a superhero is therefore pretty interesting. One might be tempted to assume that this reveals an innate goodness about Petra, a need to use her powers for peace and justice and warm woollen mittens. And in truth, knowing almost nothing about the girl, that might well be a factor, potentially the primary factor. On the other hand, there may be more to it than that, though to consider the possibilities we need to delve into the back story that I can't trace (seriously, if anyone knows where this stuff has come from, let me know in comments).
Petra and her family (her parents and her older brother) are all caught in a rock slide shortly after her thirteenth birthday. Subconsciously she uses her powers to save herself, but the other three are killed. This in itself, the "tragic past that could have been averted by knowing of one's superpowers" isn't really massively original, but in Petra's case it keeps getting worse. Given to a new family, Petra finds her foster mother to be uncaring, and her foster father to be an out-and-out sicko perve in training. When he finally attempts to fully-fledged child molester whilst in the park, Petra (who is around fourteen at this time) once again accidentally activates her powers, causing him to sink into the ground. She flees, horrified, as her foster father screams abuse at her for being a mutant "freak" (clearly a man who'd never heard about glass houses and stones). After that, she lives on the streets, begging and stealing, manipulating nearby caves to provide shelter, and constantly worrying whether she could have saved her family from the rockfall, or even if she had caused the accident in the first place. Everywhere she turns she finds anti-mutant bigotry and hate crimes. As an orphan mutant hobo, it must have seemed that there was little lower that she could sink. Complicating the issue is the possibility that the misery of being a mutant, the social stigma of being a panhandler, her guilt over her parents death, and her brush (mercifully abortive though it was) with child-abuse (the psychological after-effects of which are many and varied, and frequently pretty hideous) may have become intertwined. How could anyone expect a girl in her mid-teens to understand what feeling was generated by what experience, and how the whole mess could be untangled?
At sixteen she learns how to generate diamonds. Given her past history though, the idea of making enough of them to get rich may never have entered her head. There is likely no way she could produce wealth on such a scale without revealing herself to be a mutant, and subject herself to what she believed would be the disgust of the whole of society, as she revealed the massive snowball of guilt and inferiority that had built up over her time as a runaway. Rather than risk that, she keeps her diamonds small, and pawns them for money she uses to stay in a motel room. Eventually though she is arrested, whereupon she meets Moira after the latter woman has Petra's charges dropped, in exchange for Petra entering MacTaggert's care.
From there Petra accepts her new role as superhero in training with gusto, giving no obvious outward sign of her inner turmoil. The chance to fight for mutant-kind whilst behind a mask is one she apparently grasps wholeheartedly. Like so many others before her, her teammates and mentor seem to function as a surrogate family. This idea leads to a form of vindication in a strange and slightly twisted way, as in her final moments she and her new "family", Darwin and Vulcan, are threatened once again by a wave of rock, though this time it comes in the form of the insane and murderous "living island" Krakoa. This time her instinct is to use her power, now fully under control, to save her teammates by burying them beneath the ground, allowing them to survive as Krakoa incinerates her.
One question remains in all of this. If Petra had genuinely been so afraid that others would discover her identity as a mutant, why did she settle on the codename "Petra"? One possible answer can be found in the funeral scene at the conclusion of Deadly Genesis. Whilst both Suzanne "Sway" Chen (who died alongside Petra) and Sean "Banshee "Cassidy (who died trying to stop a now insane Vulcan in Deadly Genesis #2) have their full names and codenames written on their tombstones. Petra's, though, reads simply: "Petra, beloved comrade". If Moira had known the girl's full name, she chose to never reveal it to anyone else. Perhaps Petra had spent so long as an unknown on the streets that she felt no need for a codename any more than she did a surname. Her fear of discovery was out of immediate concern for her own well-being, rather than the more abstract fear of others knowing and cursing her name. Perhaps all the traumas and losses and escapes (physical and psychological) over her life had led her to believe that Petra was no more her name than anything else.
That's the cynical way to look at it, though. Personally, I prefer to believe that Petra's acceptance amongst her fellow mutants, and the care and devotion she received from a person like Moira, who was everything her foster mother wasn't, and everything she'd believed humans in general couldn't be, kindled a spark of hope in her, a belief that she could live a normal life, even if that normality included fighting gigantic monsters alongside time-manipulators, shape-changers, and energy-casters. Perhaps, in the final analysis, the codename "Petra" was a conscious choice to accept her past, and use it to inform the future, not to contaminate it.
I certainly hope that the latter is the case. She deserved to find peace. After all, she was an X-Man.
Next time, we investigate the history of Sway, who may have had even less to do than Petra did, but could at least boast a marginally more interesting power.
 We'll probably get into the details next time round, but the short version is that Petra's first mission went so badly wrong, and she and her teammates were apparently so totally, totally killed, that the Professor wiped all knowledge of their existence from Cyclop's mind, who was the only X-Man to know they had ever existed at all.
 Totally irrelevant fact: the Slovenian equivalent of "bought the farm" is "went picking mushrooms". See how this site is entertaining and educational. Or it would be, if anyone was likely to read an article about an X-Man that even I didn't know existed until I found a complete list of every member through the years.