I. love. gemstones. All kinds: rubies, opals, emeralds, diamonds, spinel. Over the years I've discovered new gemstones I'd never heard of (like spinel) and learned that the commercial coloring you typically see might not be the only color that gemstone has to offer.
Take sapphires for instance; you probably recognize sapphire for having a velvety blue color, but sapphire's can come in close to any color of the rainbow. Violet, pink, orange, yellow and in all different shades, light to rich.
So now let's talk which gemstones are best for your (or your significant other's) engagement ring. I tend to suggest diamond, sapphire, ruby and spinel, the reason being these gemstones are hardest on the Mohs scale -- which matters because we (your partner especially ;) hope you wear your engagement ring every day! And we want it to last you a lifetime and many lifetimes to come -- a future heirloom for generations to come.