This is a lovely large brown/black & white striped onyx agate "druzy" pendant, Marquise-shaped. It is onyx agate, with a really interesting central "druzy" section of crystalline quartz.
This one comes with an attractive copper bail and 18" brown necklace.
This stone is indeed quartz and banded agate, but it has been dyed in order to obtain the unusual coloration. These come in many variations and are indeed striking.
"Druzy Agate" is one of my favorite forms of agate. They usually have opaque, translucent, and natural quartz sections, and can be very artistic. These stones come in hundreds of variations and are indeed striking.
(As always, if you don't like the choice of bail or necklace, just contact me and we can make changes.)