Where Do Garnets Come From?

Garnet. Image courtesy of Edward Fleming Jewellery.

What are Garnets?

Garnets often bring to mind a deep-red coloured gem, easily confused with a ruby. However, not all garnets are red. It would be better, then, to consider garnet a species, a mineral group, in which there are six sub-garnets: pyrope, almandine, spessartite, grossular (ex. tsavorites), uvarovite, and andradite (demantoid). All garnets are of the silicate mineral group, a complex chemical formula including silicate. However, different varieties of garnet have different metal ions (iron, aluminium, magnesium, and chromium). These determine not only the variety of garnet, but also the colour of the gemstone, as garnets come in a wide array of colours, from the brilliant orange of spessartite to the stunning green of a demantoid garnet. The name garnet was coined by German theologian, Albrecht von Bollstadt (1193-1280) from the Latin granatus, from granum (meaning grain or seed), which refers to the seeds in pomegranates. Garnets were said to have originated from the twelve stones worn on the breastplate of Aaron. These stones were later connected to the twelve months of the year, with the National Association of Jewellers establishing the official birthstone list in 1912. As garnet is the birthstone of January, we thought we’d take this chance to look into where these lovely gemstones come from and what their uses are.

What are the Uses for Garnets?

Despite being known as a gemstone, very few number of garnets are flawless enough to be of gemstone quality. In fact, garnets have many uses aside from being made into jewellery, as big fans as we are of a nice garnet.

Many garnets are mined for industrial purposes. This includes blast-cleaning, polishing, filtration, and water jet cutting. In water jet cutting, a high pressure jet of water with garnet and other abrasive grains in it is aimed at metal, ceramic, or stone to cut it. Garnet makes an excellent abrasive due to its hardness (7.5 and 8.5 on the Mohs scale of hardness) and its resistance to weathering. Garnet is widely being used to replace silica in abrasives, as silica is dangerous to workers’ health.

In addition to abrasives, lithium oxide garnets (those with a high number of lithium atoms in the crystal structure) can be used as electrolytes for batteries, being used for rechargeable battery technologies.

Where are Garnets Found?

Garnets are found in many places throughout the world, including Brazil, Namibia, Kenya, Tanzania, Iran, Afghanistan, Pakistan, Sri Lanka, India, Russia, USA, and China. Different varieties can be found in different locations.

Almandine on grey-green schist

How are Garnets Formed?

Garnets can be found and formed in many different ways, depending on the variety. They may be found as individual crystals, pebbles, or clumps of inter-grown crystals. It depends entirely on the geological environment. Most are found where sedimentary rock with a high aluminium content is metamorphosed (subject to heat and pressure). The high pressure breaks chemical bonds in the rocks and cause the minerals to recrystalise. As a result, new minerals (including garnet) form in either schist (metamorphic rock made up of plate-shaped mineral grains large enough to be seen by the naked eye) or gneiss (metamorphic rock identified by its bands and lenses of varying mineral compositions). This commonly occurs where two tectonic plates converge. During this process, garnets start as tiny grains and enlarge slowly over time, displacing, replacing, and including surrounding rock material.

Gneiss

How are Garnets Mined?

Garnets are primarily found near the Earth’s surface, making them relatively easy to mine. However, depending on how and where they’ve formed, garnets may be mined differently.

Open Pit Mines: Open pit mines are used where concentrated soils and sediments that form when garnet-bearing rocks are weathered and eroded. These are known as alluvial garnets. Open pit mining is a surface mining technique that extracts minerals from an open pit in the ground using a varying amount of mechanisation. This method does not require extractive methods or tunnels. One such example of this is the Enegbo rutile and garnet mining project near the Ford fjord.

Open pit mine

Small Scale and Artisanal Mining: In some mines, such as those in Rajasthan, artisanal mining is used. This refers to mining done by individuals, often with minimal or no mechanisation.

Artisanal mine

Wet Sieving: Wet sieving is a mining process used to remove heavy minerals, such as garnets, from sand dunes. Large barges move along dunes and revolve the sand, capturing the heavy materials and leaving behind unwanted materials.

What are the Effects of Garnet Mining?

Unfortunately, garnet mining has a lot of unfortunate impacts, primarily on the environment

Wet sieving is conducive to the destruction of consolidated sand dune barriers. This may not seem like a big deal, but these barriers, if they were to remain intact, would otherwise help stop hurricanes, prevent costal erosion, and afford protection for ecosystems around the sand dunes.

Open Pit mining, though it doesn’t dig too deep, still strips the land of its vegetation, eliminating life at the surface. If the land is not rehabilitated, landslides and rockslides can occur without warning. In addition, open pit mining can lead to water damage, through acid mine drainage. This occurs when sulfide rich rocks are broken down, forming sulfuric acid, which dissolves nearby rock and releases dangerous metalloids into local streams and groundwater. This polluted water can then kill life along the water source for miles.

However, there have been some attempts to restore land and water sources after mining. As ethical gemstones, specifically ethical diamonds, are a rising concern, some initiatives are being introduced to help combat these issues. One such initiative is the Garnet Mine Area Reclamation Project, in which waster rock and tailings are being removed from the former mining area. To address the potential pollution of the Whitewater river, the Garnet Mine Construction Remediation of Coachella Valley Water District Property, soil stock-piles and scattered concrete debris is being removed. However, you’ll be hard pressed to find examples of garnet mines restoring vegetation, which leads us to believe these are only examples of greenwashing, which you can learn more about here and here.