Onyx and Earth Signs

[2-G]

I recently bought an Onyx crystal to wear around my neck. I wasn't exactly thinking of it's properties and what not - I just thought it looked nice. So I'm wearing it around the house - ladeedadeeda - and my mom says,"Ghia, is that Onyx?"(I didn't ask the store owner) and I said,"Err I guess." Then she said,"Don't wear it to sleep, it will give you nightmares and don't wear it to school because it amplifies feelings of negativity." Then she proceeded to tell me about how I was a Capricorn(very Earth) and how a stone like Onyx is good for grounding, but being that Earth Signs are already grounded, it would have a negative affect.

Can anyone tell me more about this stone, and is it safe for me to wear?

[Morgandria]

I'm a Virgo. I wear onyx all the time, to no ill effect. It is one of my favorite stones, and I've never heard that about it.