Honestly, as long as they meet the size requirements and are safe to have around combat I'd be surprised if they were rejected. I can't speak to other chapters, but there isn't hard rules on what they need to look like -- so as long as it does meet the hard rules (size & safety) and its probably fine. If it looks very out of genre I might encourage you to find a better physrep (ie, please don't use a cellphone as a source).
A quick google of the selenite crystal and that looks like a potentially great ice source physrep.
Its my interpretation that the source rules are intentionally very open to let you do what you feel is fun or cool for the character. If you want to embroider your character's person symbol on to something, and use that as a source - go for it. If you want to have an obvious magic crystal ball - go for it. If you want to be a "healer" with a chaos source that is a skull, go for it. If you want to have a magic talisman on a necklace - go for it.
The other vaguely relevant rule is that an item can't be tagged as two things. For example you can't use a weapon as a source (except that high magic that lets you use a staff) and a weapon. So you could have a dagger physrep that acts as a source, but you couldn't put a weapon tag on it and you couldn't use it as a weapon -- and if it was hit while you had it in hand, it'd count as hitting you. (And I'd probably encourage you to not use a dagger physrep as a source just to avoid confusion.)