Nah, not feminine in my opinion.
Thinkgeek has some great stuff.
I have a ruby this size and shape, looking for a mounting. I am considering a silver cage. And it'll probably look better than that.
It's clever. And, if your lady is really interested in Mars it's a neat bauble. But, it's not stunningly attractive.
Too feminine for a man to wear, is my original question?
Not feminine at all.
As a history geek, I'll say it's worth knowing that Mars was seen as a symbol of strength and virility. Pretty damn manly.
If you ask if its too girly, it is. Wear it with pride.
Yes, too feminine. Any pendant on a light chain looks feminine. And too arcane. No one will get it is supposed to be or represent.
Well how about with a new chain? Say a big manly one, or a ball chain (as in like dogtags)?
It's an question of proportions. A heavier chain, especially a ball chain, might just be a very good choice for you.
If you really like the Mars bead, it might be more masculine looking (and cheaper) to put it on a shorter leather or rubber strand, instead of a long and dangling chain..
Dallas, you're a funny man!