Ettringite Gemstone: Properties, Meanings, Value & More

Ettringite (pronounced EHT-ring-ite) is a natural mineral often found as white or yellow crystals. Though crystals are somewhat sought-after by collectors, ettringite is better known for its synthetic formation in cement.

Is ettringite rare? The mineral itself, not so much. But crystals are rare and cut ettringite gemstones are super rare.

In this guide, we’ll cover everything you need to know about ettringite, from its properties and powers to its prices and history.

Pictured above: Bright lemon-yellow ettringite crystals on thin matrix shard | Image credit: Rob Lavinsky, iRocks.com – CC-BY-SA-3.0

About Ettringite Stone

Ettringite is a rare clear to yellow semi-precious gemstone. What is another name for ettringite? There are a few:

• Cement bacillus

• Candelot salt

• Woodfordite

Astrologically, ettringite is a Gemini birthstone. But it’s more well-known in the cement industry.

Ettringite Concrete

The most common use (and presence) of ettringite is in cements, particularly Portland cement. The most common type of cement worldwide, Portland cement is used in stucco, mortar, some grouts, and of course, concrete.

What is ettringite formation in concrete? In the concrete world, ettringite is technically a synthetic material called a hexacalcium aluminate trisulfate hydrate.

It forms in supersulphated and Portland cements as a hydration product of tricalcium aluminate reacting with calcium sulfate or gypsum. Gypsum or calcium sulfate is a setting retarder, stopping the pourable cement from hardening too early.

However, self-leveling compounds (e.g. flooring) need moisture reduction, achieved with internal and external drying. Ettringite helps with rapid internal drying because the crystals form more quickly and hold more water than other hydrates.

So, is ettringite good or bad in cement? It depends when it forms.

Delayed ettringite formation (DEF) is bad. If it forms or reforms in already-hydrated, sulfate-containing cement, it can cause corrosion, extensive cracking, and all sorts of damage. If it’s already present in early-stage liquid cement, it’s good for controlling when the mixture sets.

Other Ettringite Uses

Besides the major uses in cement, ettringite is also useful for:

• Satin white paper coating

• Gloss-white ceramic pigment

• Mineral filler

Additionally, synthetic ettringite is beneficial for removing sulfates from water contaminated by sulfuric acid. Plus, its high ion exchange capacity, a property beneficial for waste management, has been studied for use in immobilizing toxic metals — for example, chromite ore processing residue (COPR), a byproduct of chromate production that can contaminate groundwater and farms.

Pictured above: Cluster of gemmy, sulfur-yellow to brown ettringite crystals | Image credit: Rob Lavinsky, iRocks.com – CC-BY-SA-3.0

Ettringite Specifications & Characteristics

As a hydrous (or hydrated) calcium aluminum sulfate mineral, ettringite’s formula can be written as:

• Ca6Al2(SO4)3(OH)12·27H2O

• Ca6Al2(SO4)3(OH)12·26H2O

• Ca6AI2(SO4)3(OH)12·24H2O

• (Ca6[Al(OH)6]2(SO4)3.26H2O)

The first formula listed above is accepted by the International Mineralogical Association (IMA).

The mineral is part of the eponymous ettringite group of complex calcium-metal-oxysalts with carbonate, sulfate, borate, silicate, and germanate anions.

The group also includes (among others) bentorite, siwaqaite, thaumasite, and sturmanite. Ettringite is the aluminum analogue of bentorite and the sulfate analogue of siwaqaite.

Described as “a ferric iron, boron analogue of ettringite” in its first description in 1983, sturmanite is the most similar mineral to ettringite. Distinguishing the two requires chemical analysis, specimens of the two are often mislabeled as the other, and some specimens are even mixtures of both.

Ettringite crystals are often prismatic, striated, and small without terminal faces (a.k.a. “unfinished”). The mineral also occurs as thin fibers, elongated needles, or cotton-like aggregates.

Partial or full dehydration will cause changes in ettringite, making its optic sign uniaxial positive (instead of uniaxial negative), its color white, and its transparency opaque.

Ettringite properties listed:

• Mohs hardness: 2-2.5

• Color: Colorless, white, yellow, yellow-green; Turns white upon partial dehydration

• Crystal structure: Hexagonal (trigonal)

• Luster: Vitreous (glassy)

• Transparency: Transparent to translucent; Can turn opaque upon partial dehydration from atmospheric exposure

• Refractive index: 1.470-1.491

• Density: 1.77

• Cleavage: Perfect rhombohedral on {1010}

• Fracture: Irregular/uneven or conchoidal

• Streak: White

• Luminescence: None

• Pleochroism: None

• Birefringence: 0.021

• Dispersion: Unknown

Pictured above: Radiating, prismatic, colorless ettringite crystals from Germany | Image credit: Leon Hupperichs, CC-BY-SA-3.0

Ettringite Meaning & History

Like many white gemstones, colorless ettringite can represent cleansing, clarity, and confidence. In general, ettringite symbolizes duality, new beginnings, and wisdom.

In the realm of ancient Chinese philosophy, specifically the yin and yang, ettringite is in tune with Yin energy. Yin energy is the feminine, cool-tempered, restful energy of acceptance, rather than the hot, restless, active energy of Yang.

But remember: the point of yin and yang is to remind us that a good life comes from balancing both energies.

History

Ettringite’s name comes from one of the first two recorded sources and one of its type localities: Ettringen, Germany. German mineralogist Johannes Lehmann published the first official description in 1874.

Lehmann’s description was a letter to German mineralogist Gerhard vom Rath, who had described a new hydrous calcium silicate mineral that he called “chalcomorphite” from the Eifel volcanic area in Germany in 1873.

Lehmann thought his own Ettringen specimens were chalcomorphite, but in his letter, he proved they were another new mineral he called “ettringite.”

Within the next few decades, a synthetic ettringite (hydrated calcium sulfoaluminate) was discovered in cement material.

The material was nicknamed “Candlot’s salt” after French chemist Édouard Candlot, who first discovered this form of ettringite in Portland cement and pioneered research on cement hydration.

In 1943, American geologist Alfred Oswald Woodford discovered a mineral in Crestmore, California, USA, that he couldn’t identify. Geologists Joseph Murdoh and Robert A. Chalmers published the stone’s description in 1958 with the name “woodfordite,” noting it was quite similar to ettringite.

In 1960, the IMA discredited “woodfordite,” listing it as a synonym for ettringite.

Pictured above: Three-dimensional crust of gemmy, lemon-yellow ettringite crystals with hexagonal prism habit; Charlie Key Collection | Image credit: Rob Lavinsky, iRocks.com – CC-BY-SA-3.0

Ettringite Healing Properties

As a commonly yellow healing stone, ettringite has the powers of other yellow gemstones, bringing optimism, renewed purpose, and fresh starts. It can also be used as a solar plexus or crown chakra stone.

But what are the benefits of ettringite physically?

Physical Healing

Physically, ettringite is believed to help with issues related to:

• Digestive system

• Lungs

• Blood circulation

• Heavy metal & toxin elimination

• Throat pain

Emotional Healing

Emotionally, ettringite crystals are said to raise your awareness, especially for detecting someone’s true intentions. Crystal healers recommend it for strengthening your sense of self, balancing emotions, and helping you accept the emotional ebbs and flows of life without getting swept away by them.

Ettringite Gemstone Properties

Cut ettringite gemstones are pretty rare, so they don’t have standard grading criteria. However, we’ll still go over how the typical value factors apply to ettringite:

• Color: Since yellow ettringite is more rare, it may be more valuable than the more common white or colorless crystals.

• Cut: Most ettringite crystals are difficult to impossible to facet, as they’re usually too small and soft. This means faceted gems (and cut gems overall) are rare and valuable. Lapidaries may facet specimens containing ettringite and another, more durable mineral. Much of the ettringite for sale is rough (uncut).

• Transparency: Many ettringite stones are milky, so higher transparency may mean higher value.

• Carat Weight & Size: Most of the gem-quality ettringite crystals famously come from South Africa. Since much of the ettringite material is small to even microscopic, large specimens can carry significant value.

Speaking of where it comes from, how and where does ettringite form?

Pictured above: Three rough ettringite-sturmanite specimens from South Africa

Ettringite Formation & Sources

Ettringite can form through a few methods and in various settings, but it’s actually rarer to find it formed in nature than it is to find it formed in cement.

Many natural ettringite minerals form when other minerals undergo transformation from weathering or metamorphism. As such, you’ll often find ettringite in metamorphosed limestone or xenoliths, as well as larnite crusts created via weathering.

Minerals commonly associated with ettringite include:

• Afwillite

• Calcite

• Gaudefroyite

• Gypsum

• Hashemite

• Hausmannite

• Hematite

• Hydrocalumite

• Manganite

• Mayenite

• Oyelite

• Portlandite

• Sturmanite

Geographically, where is ettringite found?

Mining Locations

South Africa is famous for producing some of the best ettringite crystals. Many of these South African stones are ettringite at the core with a coating of yellow sturmanite.

Other notable sources of ettringite crystals include:

• Germany

• New Jersey, USA

• France

• Israel

• Ireland

• California, USA

In Israel (and nearby places), ettringite is notable from the Hatrurim Formation, a unique geological formation also called the “Mottled Zone.”

Pictured above: Translucent, somewhat gemmy, bright yellow ettringite crystal | Image credit: Rob Lavinsky, iRocks.com – CC-BY-SA-3.0

Ettringite Price & Value

Though pure ettringite is rarely faceted, you can find various faceted gemstones composed of ettringite and other minerals. Almost all of these are yellow, with some colorless exceptions.

These faceted ettringite gemstones range from around $60 to $250 per carat, or around $90 to $1,200 each.

Most of the ettringite for sale is rough (uncut). Well-formed yellow ettringite crystals range from about $45 to $700 each. When these crystals are attached to hausmannite, they can be $750 to $3,500 each.

Yellow crystal clusters are lower in price, going for about $25 to $300, though some can reach $750. Ettringite druzy generally costs between $60 to $400 per specimen.

More affordable rough includes the common ettringite-sturmanite mixtures, which are around $15 to $40 at wholesale.

Ettringite Care and Maintenance

In terms of gemstone care, ettringite is more delicate than other gems. It’ll partially dissolve in water, so it’s best to keep it out of water.

However, dehydration can make ettringite opaque. Some mineral collectors coat the stone with mineral oil to prevent this, while others store their minerals next to a container holding a saturated salts solution in a closed container to maintain the proper relative humidity levels.

You can clean the stone by wiping it off with a soft, dust-free, microfiber cloth.

Is Your Heart Set in Stone on Ettringite?

While ettringite is probably more common inside the flooring or sidewalks below you, these crystals can be precious additions to a rare mineral collection or decorative space!

Buy ettringite and more exceptional gemstones today!