Many women don't want diamonds. Whether social, environmental, economic, or political, those that don't want diamonds have valid reasons. If you're in search of a diamond alternative engagement ring, you're in luck. Almost anything with the general shape of an engagement ring placed on the right finger looks right.
If you want a diamond look-alike, moissanite is my favorite diamond alternative for engagement rings. Moissanite was discovered in fragments of meteorite in the late 1800's and is now made synthetically.
A natural alternative is the white sapphire. Sapphire, like diamond is very durable. It also has valid name-recognition to the public. White sapphire, however, does not sparkle like diamond or moissanite.
Anything meaningul can be placed into the ring. Don't feel that an alternative to a diamond should look like a diamond or even be a stone. Two of my personal favorite engagement rings are tatoos. Be creative. Cheers.