Diamonds are not the only precious stones used in watchmaking

Buffy Acacia

Diamonds have plenty of amazing qualities, from their ability to split light into brilliant, flashing rainbows, to their hardness that surpasses any other material on Earth. They hold a lot of power over the human psyche because of those qualities, as well as the centuries of marketing efforts from those that mine or grow them. However, as the attitudes of haute jewellery slowly return to watchmaking trends, we’ve started seeing a grand return of beautiful coloured gemstones. If you want to make informed buying decisions, here’s what you should know about the other precious stones that aren’t diamonds.

A note on natural versus lab-grown gemstones

At first glance, the arguments for and against lab-grown stones are obvious. Of course, mined stones elicit a more romantic reaction to the natural wonder of Earth’s treasures, but lab-grown versions are chemically identical and far cheaper. There’s also labour to consider, as the processes for certifying ethical mining practices haven’t been enforced as strictly with coloured stones as they have for diamonds in the last decade, so trust becomes an important factor to avoid worker exploitation. Then again, lab-grown gems create almost five times the carbon footprint as mining, so nobody’s perfect. Watch brands usually don’t disclose whether or not their gemstones are natural or lab-grown, so you should feel free to enquire with them directly.

Sapphire and ruby

Both sapphires and rubies are varieties of the mineral corundum, which is the crystal form of aluminium oxide. The only measurable difference is that rubies are coloured red by chromium impurities, and any other colour of corundum is considered a sapphire. The colourless sapphire crystal on your watch and the red rubies that are used as bearings in its movement are both lab-grown forms of corundum, a technology that has been around since the late 1800s.

In jewellery and decorative watchmaking, sapphires are best-known for their deep blues caused by titanium and iron. The most prized blue stones are Kashmir sapphires from a now-depleted mine in Northern India, as well as Ceylon sapphires from Sri Lanka. Most natural sapphires these days are actually being mined in Australia, but they can be found all around the world. The incredible colour gradient of sapphires has most famously been displayed in Rolex rainbow bezels, in which the stones are natural. Padparadscha sapphires are especially popular at the moment, being found in Sri Lanka and Madagascar, and valued for their salmon-like pink and orange tones. They have a Mohs hardness rating of 9, making them the third-hardest mineral behind moissanite and diamond.

Emerald

Throughout most of history, the term emerald has applied to almost every green gemstone imaginable. It’s only within the last century or two that the study of gemmology has specified what an emerald actually is, and found many famous “emeralds” throughout history were actually just lookalikes. Modern standards dictate that an emerald is the green variety of beryl, coloured either by chromium or vanadium. Without those two trace elements, any greenish beryl is actually considered as aquamarine.

Something that’s absolutely unique to emeralds is that they’re often heavily included, meaning they have a lot of internal fractures or impurities that reduce their clarity. While other crystals are generally regarded as lower quality when included, emeralds are praised as having a beautiful “jardin” (French for garden). That said, truly eye-clean natural emeralds will still command huge prices because of their rarity, and almost every emerald on the market has been treated with oil to fill those fissures and improve its clarity. Lab-grown emeralds can either be totally clear or have their own jardin, depending on the manufacturing method, so it can be tricky to tell them apart. Currently, the most valued emeralds are mined in Colombia. Emeralds have a hardness of 7.5-8 on the Mohs scale, but can be regarded as delicate due to their internal fractures.

Beryl

While emeralds are a variety of beryl, there’s a lot more you should know about beryl in general. Emeralds are rare, but other varieties can actually be found under all manner of different trade names. The most common and popular is aquamarine, which is usually quite inexpensive to find with almost no inclusions. Pink-orange beryl is called morganite, white beryl is goshenite, and my personal favourite is the yellow/golden beryl known as heliodor. The least abundant form is actually red beryl called bixbite, which is approximately a hundred times rarer than emerald, but seems to be much less desirable.

Tourmaline

Tourmaline is affectionately known as the trash can of minerals because of how easily it soaks up impurities as it forms. As a result, the vast majority of tourmaline, which is actually an incredibly complicated mineral even when pure, is completely black and opaque. However, when tourmaline crystals grow in the right conditions, they can manifest a huge variety of gorgeous colours. In a similar manner to beryl, some of the most popular tourmaline colours have been given their own trade names, such as rubellite for red tourmaline. It’s also a gem that often displays strong colour zoning, and the kinds of tourmaline that range from green, to white, to pink are nicknamed as watermelon tourmaline.

Paraiba tourmaline is an electric blue-green variety that forms with manganese and copper impurities, and so far has only been found in small amounts in Brazil, Mozambique, and Nigeria. You can also sometimes recognise tourmaline by the presence of vertical striations within the stone, indicating its growth patterns in long, hexagonal crystals. It’s a relatively durable stone with a hardness of 7-7.5 on the Mohs scale.

Tanzanite

As you can probably tell from the name, tanzanite is only found in one approximately 14km² region in Tanzania. It exhibits an effect called trichroism, meaning that its colour can alternate between blue, violet, and burgundy depending on its orientation and the angle of light passing through. That effect is accentuated by geometric cuts in cushion, pear or trillion styles. It was introduced to the market by Tiffany & Co. in 1968, but has rapidly gained popularity in recent years. It’s a variety of the mineral zoisite, but other varieties have never had as much time in the limelight as tanzanite. The mining process ends up causing a lot of damage to these stones, so it’s rare to find eye-clean gemstones without fractures, and the stone itself is only between 6-7 on the Mohs scale.

Garnet

Garnets would most likely only be considered semi-precious due to their abundance, however there are many varieties that soar above the rest in value and desirability. Almandine garnets are the most common, and are usually the blood-red colour we strongly associate with them. Hessonite garnets take on more of a brown-to-orange tinge, while tsavorite and demantoid garnets are the most prized examples with bright green hues. Mint-coloured garnets that were originally discovered alongside tanzanite and ignored for decades, have only recently reached the market in beautiful cut-gem form, and have been met with adoration. The various forms of garnet can differ in hardness, but usually sit on the high end of 6-7 on the Mohs scale.

Quartz

Although it’s the most common mineral on Earth, formed from silicon dioxide, quartz deserves its fair share of attention. It’s often labelled as “rock crystal” in jewellery and watchmaking applications to remove itself from the stigma of abundance, as well as the associations with quartz watch movements. Beautiful carvings have been made out of clear quartz on watch dials, and it’s a great natural alternative to glass. Citrine is a pale yellow variety of quartz that naturally grows in large crystals, although the natural examples are quite rare. Most yellow and orange forms of quartz that are sold as citrine are actually amethyst that has been heat treated to change its original purple colour.

The microcrystalline formations of quartz can affect its clarity to be either slightly translucent where its known as chalcedony, or opaque, then known as jasper or chert. The most common type of chalcedony in watchmaking is certainly onyx, which forms in thick, distinct bands of black and white. The white is usually removed in favour of the black, which usually takes a gorgeous inky polish. Red carnelian and green chrysoprase are other kinds of chalcedony that have been used in watch decoration. All varieties of quartz tend to be around a 7 on the Mohs scale of hardness.