I'm often asked whether or not I can use another gemstone in one of my engagement rings. Let's use amethyst as an example. Although I could technically use amethyst in many of my ring designs, it's not a gemstone that's recommended for an engagement ring. Gemstones have varying degrees of hardness, ranging from more fragile stones like pearl or turquoise, up to the most durable material on earth, diamond. The reason you'll often see sapphire, diamond, and moissanite as typical stones for engagement rings is because they have far greater durability than amethyst.
Amethyst is a quartz, which ranks at a 7 on the Mohs Scale of Hardness. You can see where it falls on the scale here: Mohs Scale. Although quartz is a 7 out of 10 (with 10 being diamond) that's just "relative" hardness, or where gems fall in relation to one another. You can see from "absolute" hardness that diamond is actually 16 times harder than quartz, and sapphire (in the corundum family) is 4 times harder than quartz. Moissanite falls at a 9.25 on the Mohs, ranking higher than sapphire and ruby, beneath only diamond.
For an everyday ring that's mean to be worn daily for years, choosing a gem that's durable is important. However, there are certainly people who choose to wear other gemstones. Who doesn't love a rich purple amethyst, an earthy peridot, or an icy aquamarine? But it's important to be aware that those gems require the wearer be more careful, removing it often and never wearing it in abrasive situations (pun!). Durability is something to keep in mind if you're looking for a ring that will take less upkeep over its lifetime.
You may be thinking, "Oh no, but I have a gemstone ring I love wearing and it's not very high on the Mohs!" I don't mean to discourage you from wearing your beautiful rings. But you'll need to be extra careful with them when working with your hands and when around cleaners and solutions. You'll want to wear your gem ring more sparingly, and realize that it is more susceptible to scratching, chipping, and breaking.
Because I want to craft the most lasting ring possible, diamonds, sapphires, and Moissanites are my top choices for engagement rings. Consequently, I shy away from using other gems in my settings, and I do strongly recommend sticking with a more durable option when selecting an engagement ring.