Diamonds may dominate the engagement ring scene – in 2018 they accounted for 92% of the total value of gemstones sold in the U.S.[1] – but they are by no means the only choice. As a geologist and gem enthusiast, I can assure you there’s a world of naturally occurring gemstones beyond diamond that offer stunning beauty, durability, and fascinating geological backstories. Here we’ll dive into ten alternative engagement ring stones that any smart gemstone lover should consider – exploring what makes each unique from both a gemological and geological perspective.

Each of these gems has formed over millions of years under specific conditions beneath the Earth’s crust, endowing them with remarkable colors and properties. Many are plenty hard enough for daily wear (some nearly as hard as diamond itself[2]), and each carries its own allure – be it an unusual color-change trick, a storied royal past, or even cosmic origins. Let’s explore these ten diamond alternatives with the insight of a geologist friend sharing the inside scoop.

1. Sapphire (Corundum)

Sapphire has long been a favorite alternative to diamond – and for good reason. Sapphires are incredibly durable, rating 9 on the Mohs hardness scale (second only to diamond’s 10)[2], which means they resist scratching and can stand up to everyday wear. Geologically speaking, sapphire is simply the blue variety of the mineral corundum (aluminum oxide). In fact, sapphires and rubies are the same mineral, distinguished only by trace impurities: iron and titanium give sapphire its blue hues, while chromium produces the red of ruby[3]. All other corundum colors (yellow, pink, green, etc.) are termed fancy sapphires[3], so this gem actually offers a rainbow of options beyond the classic blue.

From a geologist’s viewpoint, the journey of a sapphire from formation to finger is fascinating. Sapphires typically form in metamorphic rocks (like marble) or in igneous settings (like basalt lava flows), often in tectonically active regions[4][5]. Over eons, weathering and erosion free the tough corundum crystals from their host rock, and rivers carry them downstream. Many of the world’s sapphires are mined from alluvial gravels – the ancient riverbeds of places like Sri Lanka, Myanmar, or Madagascar – where nature has already done the work of breaking down the rock and concentrating the gem pebbles[6]. Imagine a sapphire crystal enduring millions of years tumbling in sand and water; when you wear a sapphire ring, you’re literally adorning yourself with a survivor of Earth’s geologic processes. And if blue isn’t your color, remember sapphire comes in pink, yellow, peach, green and more, offering both beauty and bragging rights to a gem born of Earth’s dynamic crust.

2. Ruby (Corundum)

If you love the idea of a hard, durable gem like sapphire but in a fiery red color, ruby is the answer. Ruby is simply the red form of corundum, colored by traces of chromium in its crystal structure[3]. That chromium not only gives ruby its passionate red hue, but also causes many rubies to fluoresce under ultraviolet light, which can make fine rubies appear to glow with an inner fire in sunlight – a dazzling trick for an engagement stone. Like sapphire, ruby scores 9 on the Mohs scale, so it’s more than tough enough for daily wear. In fact, in ancient Sanskrit, ruby was called ratnaraj, meaning “king of gems,” prized for its hardness and intense color.

What might surprise you is just how rare and valuable top-quality rubies can be – often commanding prices higher than diamonds of equivalent size[7]. For example, the famed “Sunrise Ruby,” a 25-carat Burmese ruby, sold for a record $30+ million in 2015 (over $1 million per carat), outstripping most diamond prices[7]. Geologically, rubies form in some of the most challenging conditions: many originate in marble in places like Myanmar’s Mogok region, where specific chemistry and heat/pressure conditions align to let corundum grow infused with chromium. Like sapphires, rubies are often found in gravel deposits downstream from these metamorphic sources once nature erodes the host rock. Their extreme rarity in fine quality – vivid “pigeon’s blood” red with minimal impurities – makes them even more special as a choice for an engagement ring. If you choose a ruby, you’re not just opting for a romantic red gem; you’re joining a tradition of passion and prestige that spans cultures and centuries, from ancient kings to modern collectors.

3. Emerald (Beryl)

Maybe your heart is set on green – deep, lush green that evokes life and renewal. In that case, skip the diamond and consider an emerald, the classic green variety of beryl. Emeralds have been adored from Cleopatra’s time to modern brides, and their rich green color comes from traces of chromium or vanadium in beryl’s mineral structure[8]. On the Mohs hardness scale, emerald falls around 7.5–8[9] – reasonably hard, though notably softer than sapphire or ruby. However, most emeralds contain many internal inclusions (poetically called “jardin”, or garden, by gem lovers) and tiny fractures, which can make them more brittle. A geologist will caution that emeralds are not as tough as their hardness suggests, so ring settings should protect the stone and you’ll want to wear it with a bit more care.

What makes emerald truly fascinating is how rare its geologic recipe is. To form an emerald, nature needs a very unusual convergence of ingredients: beryllium (a rare element usually found in pegmatites or granitic rocks) must meet chromium or vanadium (typically found in ultramafic or sedimentary rocks) under the right conditions. Emeralds are “unusually rare because their formation requires elements from entirely different depths within Earth’s crust.”[10] It’s a bit like two geologic realms (deep granitic intrusions and shallow crustal rocks) had to collaborate to grow this green gem. Often this happens along major fault zones or where hot hydrothermal fluids carry beryllium into contact with chromium-rich rocks[11][12]. The result is that emerald deposits are few and far between – think Colombia’s Muzo and Chivor mines, Zambia’s Kafubu area, or Afghanistan’s Panjshir Valley. Unlike sapphire or ruby, you won’t find emeralds washing about in river gravel; they’re too fragile and typically break apart during weathering, so they must be mined from the hard rock source[13]. For your engagement ring, that means each emerald is a rare geologic marvel – a testament to just how special and improbable Earth’s treasures can be. The verdant green and intriguing inclusions of an emerald stone also give it an old-world character and warmth that manufactured gems can’t replicate.

4. Morganite (Pink Beryl)

A bluish-green aquamarine crystal from Brazil (beryl family) is shown above. Morganite, by contrast, is beryl’s pink variety, colored by traces of manganese. Morganite has become a darling of modern brides who want something different, thanks to its delicate blush-pink hue and attractive sparkle. Morganite is the pink to peach variety of beryl, the same mineral family that includes emerald and aquamarine[14]. Its lovely pastel color – ranging from soft pink to rosy peach – is caused by a trace of manganese impurities in the beryl crystal lattice[15]. In terms of hardness, morganite is identical to emerald and aquamarine, about 7.5–8 on Mohs scale[16], which is sufficiently hard for regular wear (though, like all beryls, it’s wise to avoid rough knocks).

What a geologist finds intriguing about morganite is the typical environment it forms in: pegmatites. These are coarse-grained igneous rocks that form when magma cools slowly and leftover elements concentrate into exotic minerals. Pegmatites are like nature’s gem factories – and morganite often grows as gorgeous hexagonal crystals in these pockets, sometimes alongside other gems like tourmaline or kunzite. Major sources include Brazil (particularly Minas Gerais), Madagascar, Afghanistan, and even parts of California. Morganite was actually named after financier J.P. Morgan in 1911 by gemologists at Tiffany’s (to honor his gem-collecting philanthropy), so it has a bit of Gilded Age history behind it as well[17]. In an engagement ring, morganite offers a romantic vintage vibe: its soft pink tones flatter many skin tones and pair beautifully with rose gold settings. You get the geological pedigree of a natural beryl gemstone, but in a unique color that stands out from the usual white diamond – often at a much more accessible price. Just remember that morganite’s gentle color can be subtle in smaller stones (strong pink shades are rare unless the stone is fairly large[15]), so to make the most of its beauty, you might choose a slightly larger or well-cut stone that emphasizes its rosy glow.

5. Alexandrite (Color-Change Chrysoberyl)

If you’re the indecisive type – or simply love a good party trick – alexandrite might steal your heart. This gem has been called “emerald by day, ruby by night” for its astounding ability to change color under different lighting. A fine alexandrite appears greenish or bluish in daylight and then turns purplish red under incandescent light – essentially giving you two gems in one. This isn’t magic but pure geology: alexandrite is a variety of the mineral chrysoberyl (BeAl₂O₄) that contains traces of chromium. The chromium causes it to absorb light differently in incandescent (warm, red-rich) versus daylight (blue-rich), leading to a dramatic color shift. According to the USGS, alexandrite appears green in daylight and red under incandescent light[18] – a phenomenon that never fails to wow viewers.

Discovered in Russia’s Ural Mountains in the 1830s and named after the future Tsar Alexander II, alexandrite is exceptionally rare. Classic Russian alexandrites are scarce now; most gem-quality alexandrite today comes from Sri Lanka, East Africa or Brazil, often in smaller sizes. But a natural alexandrite of decent size with a strong color change is among the most coveted (and expensive) gemstones in the world. For an engagement ring, an alexandrite is a conversation starter: by day it might look teal or greenish, and by your romantic candlelight dinner it will flash purplish-red tones. It’s also quite a durable stone – chrysoberyl ranks 8.5 on the Mohs scale[19], so only sapphire and diamond are harder – which gives peace of mind for daily wear. The mystique of alexandrite is that it embodies duality; it reminds us that nature can be full of surprises. One moment it’s cool and calm, the next it’s warm and passionate. If that resonates with you and your partner’s dynamic, alexandrite might just be the ultimate geological metaphor in ring form.

6. Spinel

Red spinel is the ultimate under-the-radar gemstone – once mistaken for rubies by kings, now a favorite of gem connoisseurs. Spinel comes in a variety of colors (red, hot pink, blue, lavender, even black), but its crimson red variety historically fooled many into thinking they’d found giant rubies. Case in point: the famed “Black Prince’s Ruby” in the British Crown Jewels is actually not a ruby at all, but a 170-carat red spinel that has adorned England’s Imperial State Crown for centuries[20]. Imagine the shock of modern gemologists discovering that some crown “rubies” were imposters – spinel had been hiding in plain sight!

From a scientific perspective, spinel (MgAl₂O₄) is a magnesium aluminum oxide that crystallizes in the cubic system. It has a Mohs hardness of 8[21], which means it’s quite hard and suitable for engagement rings (only a bit softer than sapphire and much harder than an emerald). One advantage of spinel is that it often forms with excellent natural clarity – and unlike ruby or sapphire, spinel is typically not treated, so what you see is entirely natural. Fine red spinel can possess a pure, neon glow (often a slightly pinkish-red) that many actually prefer to rubies, and at a fraction of the price. There are also gorgeous blue spinels (some with a cobalt-blue hue) and vibrant hot pink spinels that can rival pink sapphires.

Geologically, spinel often occurs in the same neighborhoods as corundum. In places like Myanmar, Sri Lanka, and Tanzania, you’ll find spinel in marble or alluvial deposits right alongside rubies and sapphires. The historical confusion is understandable – before modern mineralogy, any pretty red stone was labeled “ruby.” In fact, red spinel was historically called “balas ruby”[21] and valued highly in its own right by savvy traders. Today, spinel is experiencing a renaissance as people rediscover this once-overlooked gem. Choosing a spinel for an engagement ring says you value rarity and character. It’s a gemstone with a story (just ask the British Crown), and thanks to its excellent hardness and brilliance, it will sparkle in your ring as brilliantly as any ruby or sapphire. Plus, you get the fun of explaining that your ruby-red stone is actually a spinel – a bit of gemological trivia that sets you apart from the crowd.

7. Tanzanite (Blue Zoisite)

Tanzanite is the newcomer on this list – a gem that literally goes beyond diamond in rarity, being found in only one place on Earth. As its name hints, tanzanite comes exclusively from Tanzania, East Africa. In fact, the Merelani Hills of northern Tanzania are the unique locality in the world for gem-quality tanzanite[22] – a deposit just 7 km by 2 km in size. If supply rarity excites you, consider this: tanzanite is often said to be 1000 times rarer than diamond because of its single-source geography. Discovered in 1967 (and famously popularized by Tiffany & Co. shortly after), tanzanite is a relatively young gem in the market but has skyrocketed in popularity for its mesmerizing blue-violet color.

What is tanzanite, mineralogically? It’s a calcium aluminum silicate called zoisite, and in its pure form zoisite isn’t blue. Tanzanite’s stunning blue-violet hue comes from trace amounts of vanadium in the crystal structure[23]. Heat treatment (either by nature or by man) enhances the blue by adjusting the oxidation state of vanadium and titanium in the stone[23]. The result is one of the most striking gemstone colors in the world – a rich velvety blue with flashes of purple, often shifting slightly in different lighting. In fact, tanzanite is trichroic, meaning it can show three different colors when viewed from different crystal directions (blue, violet, and burgundy) due to the crystal’s pleochroism[24]. Skilled gem cutters orient the stone to showcase the best blue face-up.

Now, an important note for rings: tanzanite is moderately hard (around 6.5 on Mohs) and has distinct cleavage, which means it can be chipped or scratched more easily than, say, sapphire. So if you choose tanzanite for an engagement ring, a protective setting (like a halo or bezel) is wise and you’ll need to treat it a bit more gently. That said, many people happily wear tanzanite rings daily – just be mindful it’s not as rugged as the corundum family. But what you get in exchange is a gem of singular rarity and beauty. Each tanzanite carries the exotic cachet of its sole Tanzanian birthplace; it’s like wearing a piece of the African night sky. For those who love a great origin story, tanzanite delivers: forged in the heat of regional metamorphism in the “Gemstone Belt” of East Africa[25], this gem went unknown to humankind for millennia until a Maasai tribesman (so the legend goes) stumbled upon crystal chunks shimmering blue in the foothills of Kilimanjaro. Talk about a romantic backstory for a stone symbolizing your once-in-a-lifetime love.

8. Tourmaline

If you crave color, tourmaline is like a candy shop of choices. Tourmaline isn’t a single mineral but a whole family of related minerals (complex borosilicates) that come in an astonishing palette of colors – often multiple colors in the same crystal. This is the gem that can be watermelon-colored (pink center, green rim), neon electric blue, mint green, golden yellow, bubblegum pink, or nearly any hue in between. In fact, tourmaline’s name stems from “turmali,” a Sinhalese word meaning “mixed gems,” because traders in Sri Lanka found so many different-colored stones that all turned out to be tourmaline. On the practical side, tourmaline’s hardness is about 7 to 7.5[26], which is decent for a ring stone (comparable to quartz or garnet). Many tourmalines are quite free of inclusions, yielding eye-clean gems with bright sparkle.

Geologically, tourmaline typically forms in pegmatites (like morganite does) or in metamorphic rocks. Those slow-growing environments allow tourmaline crystals to incorporate various metal ions that produce different colors. For example, iron-rich tourmalines are often deep green or blue, magnesium-rich ones can be brown to yellow (dravite), and manganese yields pink to red (rubellite). There are special varieties named for locales or colors: Paraíba tourmaline is a rare neon blue-to-green variety from Brazil (and also Nigeria/Mozambique) made vivid by traces of copper – it stunned the gem world in the 1980s and remains one of the most sought-after and expensive gems. Rubellite is the term for vivid pink or red tourmaline, prized for its almost glowing color. Indicolite refers to beautiful blue tourmaline[27]. You can even get chrome tourmaline (intense green colored by chromium) rivaling emerald, or parti-colored tourmalines that blend two or more tones (like pink-green watermelon tourmaline).

One really cool property of tourmaline that a geologist friend would geek out about: it’s pyroelectric and piezoelectric. This means a tourmaline crystal can accumulate an electric charge when heated or put under pressure. In fact, tourmaline’s pyroelectric behavior has been known since antiquity – ancient scientists observed that heated tourmaline would attract ashes or small bits of paper, behaving almost like a magnet[28]. While that’s not directly relevant to wearing it in jewelry, it’s a fun scientific trivia to attach to your ring (“my ring could technically generate an electric charge!”). In an engagement ring, a well-chosen tourmaline offers a combination of beauty and individuality. Because tourmaline comes in so many colors, you can pick one that perfectly symbolizes your beloved’s personality or perhaps a birthstone (October’s birthstone is tourmaline). Just avoid extremely included stones or overly soft varieties, and your tourmaline ring will hold up well. With tourmaline, you truly get a bespoke choice – it’s Mother Nature’s artistic palette captured in crystal form.

9. Zircon

No, not cubic zirconia – we’re talking natural zircon, an ancient and greatly underrated gemstone. Zircon is actually one of the oldest minerals on Earth; the oldest zircon crystals (from Western Australia) have been dated at about 4.4 billion years old[29], almost as old as the Earth itself! While those ultra-ancient zircons are microscopic grains used by geologists for dating rocks, the zircon gem you’d put in a ring is still a piece of that primordial heritage. Zircon (chemical formula ZrSiO₄) occurs in a range of colors: blue is the most popular for jewelry, but it also comes in clear (colorless), golden yellow, red, brown, and even green. One of zircon’s superpowers is its brilliance and fire – it has a high refractive index and strong dispersion, meaning a well-cut zircon sparkles fiercely and displays rainbow flashes of color much like a diamond. In the days before synthetic cubic zirconia existed, colorless zircon was actually used as a diamond simulant and was sometimes misleadingly sold as “Matura diamond”[30]. Even today, a fine colorless zircon can scintillate so much that it might fool the untrained eye at a glance.

From a durability standpoint, zircon has decent hardness (about 7.5 on Mohs scale)[30], similar to quartz, but it does have a brittle streak. Natural zircon crystals often contain internal stress (some have partially broken down over geologic time due to radiation from trace elements), so cutters tend to facet them with care. Once set in jewelry, zircons can be worn daily, but avoid rough impact as they can chip. That said, with reasonable care, a zircon engagement stone can last generations – after all, it already survived a few billion years in the Earth! Blue zircon, with its vibrant teal or sky-blue color, is a popular diamond alternative for those wanting a burst of color. It’s worth noting that most blue zircons on the market have been gently heat-treated to achieve that color from brownish rough. This is a stable treatment and widely accepted in the gem trade. If you prefer something warmer, golden-orange “hyacinth” zircons have a lovely autumnal glow.

Choosing zircon is a subtle nod to geology – you’re picking a gemstone that carries deep time in its crystal lattice. In a poetic sense, giving a zircon ring could symbolize a love that is as enduring as the ages. And for the scientifically inclined, you can marvel that the gemstone on your finger likely formed in Earth’s crust when it was still young, possibly when the first continents were just starting to solidify. How’s that for romantic nerdiness? Plus, you get all this charm in a gem that, thanks to being underappreciated, often costs far less than tourmaline, sapphire or other alternatives. A zircon may not be as famous as a diamond, but it offers an illustrious sparkle and a connection to Earth’s deep history that few gems can match.

10. Moissanite (Silicon Carbide)

Our final pick isn’t a traditional “gemstone” that you dig from the earth in large crystals – but it is a naturally occurring mineral, with a truly out-of-this-world origin story. Moissanite is silicon carbide (SiC), a substance first discovered in 1893 by chemist Henri Moissan in rock samples from a meteor crater in Arizona. That’s right: the original moissanite came from a fallen star (the Canyon Diablo meteorite), making it literally a space gem. Natural moissanite is exceedingly rare on Earth, but today we have the technology to create moissanite crystals in the lab that are large enough and flawless enough for jewelry. These lab-grown moissanites have become one of the most popular diamond alternatives, prized for their high sparkle and ethical, sustainable sourcing (no mining needed).

So why do gemologists and savvy couples love moissanite? For one, it’s nearly as hard as diamond – about 9.25 on the Mohs scale, sitting between corundum (sapphire/ruby at 9) and diamond (10)[31]. This means moissanite is extremely durable for a ring; you can wear it daily without worry of scratching. Secondly, moissanite has some optical properties that even exceed diamond. It has a higher refractive index than diamond, which gives it extraordinary brilliance, and a higher dispersion too, meaning it can exhibit more fiery rainbow flashes under light[32]. In plain terms, a well-cut moissanite can out-sparkle a diamond – it tends to throw more rainbows. Some people find this extra fire very appealing (though it’s a slightly different look than a diamond’s more steely brilliance). Moissanite also has a high luster. All these qualities led the USGS to call moissanite “an excellent diamond simulant” that is marketed for its own gem qualities, with greater brilliance and luster than diamond[32].

From a geologist’s perspective, it’s fun to note that while your moissanite ring stone grew in a lab, its composition is the same as those tiny silicon carbide crystals that arrived in meteorites from space. Silicon carbide does not form easily in Earth’s oxidizing environment, but it can form in certain star systems and was delivered here by asteroidal collisions – talk about a cosmic connection! Using moissanite in an engagement ring is also a practical win: you get diamond-like appearance at a fraction of the cost, and you’re not tapping into gemstone mining at all. Many eco- and budget-conscious couples appreciate that moissanite is conflict-free and lab-grown, yet chemically and visually stunning. It’s not “fake” – it’s a real mineral with its own name and identity, just not one that’s traditionally been available in large sizes from nature. When you look at a moissanite, you’re seeing what decades of technological innovation and a bit of stardust magic can create. And since moissanite’s hardness and stability are so high[31], this stone is poised to remain just as brilliant on your 50th anniversary as on day one. In short, moissanite offers the best of both worlds: the durability and dazzling sparkle of a diamond, and a unique origin story that goes beyond the Earth – quite fitting for a symbol of a love that’s out of this world.

In Conclusion: Choosing an engagement ring stone “beyond the diamond” opens up a treasure trove of colors, histories, and scientific marvels. Whether you gravitate toward the legendary blues of sapphire, the verdant rarity of emerald, the chameleon magic of alexandrite, or the meteoric sparkle of moissanite, you really can’t go wrong – it’s about finding the gem that speaks to you. Each of these alternatives has been celebrated by gemologists and geologists alike for its natural beauty and durability, as we’ve seen through the reliable sources and research above. By considering a non-diamond center stone, you’re not just making a style statement; you’re also celebrating the rich geodiversity our planet (and even outer space!) has to offer. After all, an engagement ring is deeply personal – why not choose a gem with a story as unique as your own? From the depths of the Earth to the far reaches of history and space, your perfect stone is out there shining, just waiting to be discovered.

Sources:

[1] [31] [32] Gemstones 2018 https://pubs.usgs.gov/myb/vol1/2018/myb1-2018-gemstones.pdf

[2] [18] [19] [21] [26] [27] [30] Natural Gemstones – Mineral Gemstoneshttps://pubs.usgs.gov/gip/gemstones/mineral.html

[3] [4] [5] [6] [7] [13] Layout 1https://www.gia.edu/doc/WN19-geology-of-corundum-and-emerald-gem-deposits.pdf

[8] [9] [10] [11] [12] EMERALDS https://www.deq.nc.gov/energy-mineral-and-land-resources/geological-survey/geoscience-education/emeralds/open

[14] [15] [16] [17] What Is Morganite Gemstone | Morganite Stone – GIA https://www.gia.edu/morganite

[20] Black Prince’s ruby | Royal Jewel, Crown Jewel, British Crown | Britannicahttps://www.britannica.com/topic/Black-Princes-Ruby

[22] periodico https://rosa.uniroma1.it/rosa04/periodico_di_mineralogia/article/download/15797/15170

[23] [24] [25] Tanzanite: A Rare Blue Beauty | Geology for Investors https://www.geologyforinvestors.com/tanzanite-a-rare-blue-beauty/

[28] (IUCr) Structural mechanism of pyroelectricity in tourmaline

https://journals.iucr.org/paper?a14257

[29] Jack Hills Conglomerate from Western Australia | U.S. Geological Survey https://www.usgs.gov/media/images/jack-hills-conglomerate-western-australia