I’m going to propose to my gf in a few months and I need an idea for a stone for the engagement band.
she is (bless her heart) vehemently opposed to purchasing diamonds because of the debeers cartel and their history of naughtiness.
I was thinking something with a purple/lavender hue (her fav color).
any suggestions?
Your best bet is a sapphire.
There are many beautiful stones out there for engagement rings, but for a ring she’ll wear every day, you want something as close as possible to the hardness and sturdiness of a diamond…and a sapphire is a 9 on Moh’s scale, vs. a ten for a diamond.
Sapphires also come in many shades of blue, so with luck you should be able to find something in a hue you know she’ll love.
I personally really love Tanzanite, which is a lovely purple-lavender color…but it’s, relatively speaking, rather soft for a stone that will have all the wear and tear of an engagement ring.
You might also think about Moissonite; it’s a white stone, like a diamond, but it reflects the entire color spectrum, so it’s many times more brilliant than a diamond…and the chemical compound for it was discovered in a meteorite in Nevada. It’s a 9.25 on Moh’s scale, only slightly softer than a diamond. Frankly, I just like the idea of a stone from outer space. 
Oooo, I’ve never heard of moissanite before. Look how pretty!
In lieu of that (if that’s not an option – I have no idea what the cost is or what your budget is), I second the nomination for a sapphire. That would be my next favorite stone for an engagement ring.
Moissanite is way cool. If you get a reasonably sized one (~1 carat) it’s relatively inexpensive, comparatively speaking - and then you can go all out on a really unique setting for it. Maybe even design something together and have it made.
Just for your easy reference, here’s a related thread: Questions about buying an engagement ring
For very nicely priced deals on all kinds of stones, try Thaigem.com. You can search by color and price as well as shape and all kinds of other variables, and they’ll do custom settings. They have some good gemological information and very clear pictures, so you can also use their site to start learning more about something to buy elsewhere. If you do decide to buy something from them, I can vouch for their excellent service.
Oh, and by the way, if your sweetie is politically conscious enough to resent deBeers, she might like a lab-crated stone, since those aren’t mined by exploited labor etc.
As maybe you already know, “lab-created” stones are not fakes in the way that cubic zirconia is fake diamond, nor substitutes – they’re minerologically the same as mined stones, but made on purpose under controlled conditions. Gemologists can tell them apart from natural ones but almost no one else can.
One exception would be lab-created opals, which do look visibly different from natural ones.
Oh, and by the way, if your sweetie is politically conscious enough to resent deBeers, she might like a lab-created stone, since those aren’t mined by exploited labor etc.
As maybe you already know, “lab-created” stones are not fakes in the way that cubic zirconia is fake diamond, nor substitutes – they’re minerologically the same as mined stones, but made on purpose under controlled conditions. Gemologists can tell them apart from natural ones but almost no one else can.
One exception would be lab-created opals, which do look visibly different from natural ones.