Yeah, but since opals can be up to 21% water, they’re as fragile for rings as, well, as some of the love stories we’re hearing in this thread!! 
I love opals. Great for necklaces. Go with the sapphires. Can’t go wrong.
After 10 years together, my husbear and I moved to California and had a commitment ceremony to celebrate a decade together. I had white gold rings with an Australian opal on an onyx base. One stone got cracked early on and was replaced. We both have worn them daily for the last twenty years.
I just asked for and got an onyx ring. Because I am a black-hearted bitch.
I’m on my 3rd “wedding” ring because I break rings. He has never minded because it meant I was actually washing dishes or something.
<3 Been married 25 years.
As others have said, if this is for a loved one, then their opinion matters far more than the actual stone itself.
You can buy a large expensive diamond and be told you’ve wasted money that should have gone to a house / holiday. 
You can buy an imitation stone that looks great, but when she eventually finds out, you’re toast. :smack:
You can buy a decent-sized good value diamond and find out she just doesn’t like it. :eek:
True story - in the 1950s in the UK things were tight (e.g. we still had some rationing.)
My Dad bought my Mum an inexpensive (= cheap) simple ring as it was all he could afford.
She wore it for 60 years and would never take it off because it meant so much to her.
It occurs to me that if we take you at your word here, your best bet is to look for a big-assed industrial diamond. MUCH less expensive, carat-for-carat, than gemstone-quality.
Well, value would be determined by what you actually get compared to the price paid. So while the market sets the price, value is subjective and determined by the individual.
I suggest pawn shops. You’ll almost always get a bargain, most are far more concerned with the precious metal than the stone, be sure to ask to see anything they might be about ready to sell as scrap.
You can often find some great stones In rings or ear-rings that have de-plated spots and other ugliness. Some shops are good at maximizing their return on jewelry for various reasons and some are not, so every shop you go into will be a different market.
For many the extent of their diamond knowledge is using an electronic grader and measuring points to estimate carat weight. Find one with an older woman involved and they are usually hesitant to scrap anything, which means big selection and usually items priced largely by how long they’ve been there more than any other factor.
If I were the dude, I’d have walked as soon as she refused his grandmother’s ring. She’s more interested in things than him.
Before my current wife and I were engaged, I showed her my mother’s diamond ring and suggested having it put in a new setting for her engagement ring. She didn’t look impressed. She said wearing someone else’s diamond would be like wearing their used underwear. Point made.
<blink blink>
Not saying that people aren’t entitled to their own personal preferences about new versus pre-owned jewelry, for any reason or no reason, but that simile is pretty absurd.
The fundamental reason we object to wearing other people’s used underwear is because it’s unsanitary, and the cost savings over buying new are negligible. Neither of those observations applies to wearing (inherited or gifted) pre-owned precious stones.
Remember years ago reading a magazine article about the diamond business. It had these words of wisdom.
'Just remember that almost every new bride gets a diamond, and almost every new bride gets a dishwasher. It’s obvious - diamonds are just about as rare as dishwashers."
I sure hope he got a clue and cut her loose. That kind of attitude doesn’t make for a happy marriage.
Diamonds definitely have industrial uses; more than 99% of them are indeed used for this purpose.
Then why not buy a used one? Based upon your beliefs you should be able to purchase a used diamond for next to nothing. You get the diamond you need, without paying an exorbitant amount.
Addressed in post #48, when I looked the selection was limited. People just don’t sell used diamonds, and if they do they quickly get recycled back into the “new” diamond stream.
In any case, this thread is over a year old and I never updated it. Ultimately I went to a diamond dealer and bought a mined diamond. I essentially payed a premium for the ability to look at what I was buying and pick it out from a selection, which is hard to do with used or cultured diamonds purchased over the internet. I came real close to buying online, but backed out each time because I was worried about getting something in the mail and being unhappy with it.
Not used, “vintage.” And are you sure your thing even wants a diamond as opposed to, say, a sapphire? Not everyone who wants a big rock even wants a diamond.
And, if your “thing” is in her mid-30s or older, point out that Princess Di’s engagement ring was a sapphire, not a diamond.
“Some dead woman’s ring”? Real classy that one, a real keeper :rolleyes: