Tephroite Gemstone: Properties, Meanings, Value & More

Tephroite is a commonly gray or reddish-brown variety of olivine. Mostly known among collectors, tephroite is most famous from New Jersey, USA.

Tephroite is actually the rarest mineral in the olivine group and cut tephroite gemstones are even rarer.

Here at Gem Rock Auctions, we have a soft spot for rare, unusual gemstones like tephroite. We’ve learned over our decades of experience that no stone is worth overlooking!

That’s why we’re breaking down everything you need to know about tephroite, from its properties and uses to its history and prices.

Pictured above: Reddish-brown, partly transparent tephroite crystals associated with clear, doubly terminated willemite | Image credit: Modris Baum, Public domain

About Tephroite Stone

Tephroite is a rare semi-precious gemstone named for its ash-gray color. However, it’s also found in shades of red, brown, blue, green, and orange. In thin sections, it can be light green or colorless.

Other monikers for tephroite are:

• Tefroit

• Manganese Peridot

• Mangan-Peridot

• Mangan Olivine

Given its rarity, there aren’t many industrial tephroite uses. One exception: its use as a powerful catalytic for polymerizing polyphenols like hydroquinone to humic acids.

More often, scientists have researched tephroite to study its geologic properties like its stability relative to manganosite and rhodochrosite.

Another study examined tephroite’s behaviors under high-pressure, high-temperature conditions based on tephroite inclusions within diamonds found in ophiolites.

Many other studies on tephroite explore its relationship to other olivine group minerals.

Tephroite Specifications & Characteristics

As a manganese silicate, the formula for tephroite is Mn2+2(SiO4) or Mn2SiO4. The first formula is approved by the International Mineralogical Association (IMA).

Common impurities in tephroite include iron, zinc, calcium, and magnesium.

The mineral is in the olivine group, which are simple orthosilicates/nesosilicates with the formula M2SiO4 where M can be calcium, iron, manganese, nickel, or magnesium.

In the olivine group, tephroite is the manganese endmember. It forms two series: one with fayalite (iron endmember) and one with forsterite (magnesium endmember, known for peridot variety). As such, divalent iron or magnesium may replace manganese in the series.

In terms of habits, tephroite crystals may be elongated or short and prismatic. However, tephroite rarely forms distinct crystals.

It can occur as disseminated, anhedral, and equidimensional grains, as well as the more common masses.

Twinning can happen on {011} but it’s uncommon.

Despite being non-metallic, tephroite is heavy, with a high density. Its optic character is biaxial (-).

Tephroite properties:

• Mohs hardness: 6

• Color: Brown, reddish-brown, flesh-red, blue-green, green, olive, gray

• Crystal structure: Orthorhombic

• Luster: Vitreous or greasy

• Transparency: Translucent to opaque, rarely transparent

• Refractive index: 1.770-1.825

• Density: 3.87-4.12

• Cleavage: Distinct/good on {010}, Imperfect on {001}

• Fracture: Irregular/uneven or conchoidal

• Streak: Pale gray

• Luminescence: None; Often attached to fluorescent minerals

• Pleochroism: Sometimes present; Weak to distinct; Brownish-red to reddish to greenish-blue

• Birefringence: 0.037-0.047

• Dispersion: r > v

• Optical effects: Color-changing (very rare)

Types of Tephroite

The only varieties, per se, of tephroite both contain magnesium:

• Magnesium-Bearing Tephroite: Contains some amount of magnesium; AKA magnesian tephroite

• Pictotephroite: Contains up to 18.11 percent magnesium oxide (MgO); Found in Pajsberg, Sweden

Pictured above: Brown tephroite crystals with varying luster and habits; Charlie Key collection | Image credit: Rob Lavinsky, iRocks.com – CC-BY-SA-3.0

Tephroite History

German mineralogist Johann Freidrich August Breithaupt first described tephroite in 1823. German physician, chemist & mineralogist Karl Friedrich August Rammelsberg provided another important description of tephroite in 1843.

Breithaupt named the stone “tephroite” from the Greek term τεφροζ (tephros) meaning “ash-colored” for the specimens’ commonly gray coloring.

The specimens Breithaupt studied were from the collection of Dr. H. Heyer.

These original specimens came from the Sterling Hill mine in New Jersey, USA, now tephroite’s type locality.

At the type locality, tephroite is found associated with several minerals, including zincite, willemite, rhodonite, calcite, diopside, and more.

Tephroite didn’t enter the gem world until 1991, when tephroite crystals in South Africa that were facetable were first reported.

Tephroite Healing Properties

As an often gray or red healing stone, tephroite has the grounding, motivating, and protective properties associated with grey gemstones and red gemstones.

All tephroite stones can be used as root chakra stones.

Crystal healers recommend tephroite crystals for:

• Releasing toxins

• Boosting metabolism

• Improving eyesight

• Alleviating envy or resentment

• Inducing restful sleep

• Manifesting success

Pictured above:  Brown prismatic tephroite crystals with very good to matte luster associated with andradite garnet; Charlie Key collection| Image credit: Rob Lavinsky, iRocks.com – CC-BY-SA-3.0

Tephroite Gemstone Properties

Besides rarity, tephroite’s value also depends on color, cut, clarity/transparency, and carat weight.

Color

Despite its ash-gray etymology, many tephroite stones are found in shades of red, like pink, reddish-brown, or flesh red. This red coloring may be caused by franklinite inclusions.

Collectors are often after well-formed gray to grayish-blue crystals.

Most valuable are the extremely rare color-changing tephroites, which change from bluish-gray or grayish-green to reddish-brown in daylight and incandescent light, respectively.

Cut

Few tephroite crystals are faceted, partly because distinct crystals are so rare but also because they’re often fractured or opaque.

However, massive tephroite specimens from Australia and New Jersey can be cut into cabochons. Many tephroites for sale are rough (uncut).

Clarity & Transparency

Clarity describes the degree of visible inclusions in a gem, which can lower its transparency and value. You’ll often see inclusions of other minerals like franklinite in tephroite crystals.

Tephroite can be transparent, but it's rare — most crystals are opaque. Higher degrees of translucence or transparency is more valuable.

Carat Weight & Size

Distinct tephroite crystals are always small; thus, faceted tephroites are also small, usually under 4 carats when translucent. Some lapidarists may facet larger gems from opaque material.

Massive tephroite can be larger, yielding cabochons up to 20 carats.

Pictured above: Tephroite and cerite museum specimens from Sweden | Image credit: Nkansah Rexford, CC-BY-SA-3.0

Tephroite Formation & Sources

Tephroite minerals are only found in iron-manganese skarns and iron-manganese ore deposits, along with manganese-rich rocks or sediments that underwent metamorphism.

Minerals commonly associated with tephroite are:

• Alleghanyite

• Banalsite

• Bustamite

• Calcite

• Diopside

• Franklinite

• Gageite

• Garnet (Spessartine and Andradite)

• Glaucochroite

• Jacobsite

• Manganocalcite

• Pyroxmangite

• Rhodochrosite

• Rhodonite

• Willemite

• Zincite

Geographically, where is tephroite found?

Mining Locations

The best location for cuttable tephroite material is the mineral’s first known source: New Jersey, USA. The only other known source of cuttable tephroites is Australia.

Other tephroite sources worth noting are:

• Australia

• Antarctica

• Brazil

• France

• Italy

• Japan

• South Africa

• Sweden

• UK (England, Wales)

• USA (California, Colorado, North Carolina)

Notably, many Australian tephroite specimens are found as massive streaks in rhodonite.

Pictured above: Tephroite specimen from Kaao Mine in Japan, dated 1816 | Image credit: Dave Dyet, Public domain

Tephroite Price & Value

Faceted tephroite gemstone prices range from about $15 to $50 per carat or $40 to $150 total.

Tephroite cabochons in regular shapes are around $1-2 per carat or about $20 total.

Carvings are usually in rectangular tablet shapes and generally cost $150 per carat.

Rough tephroite specimens are quite affordable. Most specimens for sale are tephroite with other minerals like franklinite, willemite, and/or zincite. The prices mostly vary by size, ranging from around $2.50 to $75.

Tephroite Care and Maintenance

Luckily, tephroite gemstone care is pretty easy. Just be careful to avoid sharp blows, given its distinct cleavage.

Clean tephroite with warm water, mild soap, and a soft toothbrush.

Store separately from other gems to avoid scratches.

Tempted by Tephroite?

Tephroite is one of the rarest and least-known members of the olivine group, but why should olivine gems like peridot take all the limelight? Not only is tephroite a fascinating stone with unusual properties like its heaviness and rare color-changing effects, but it’s also a grounding addition to any space with its gorgeous earthy vibes.

Whether you’re a committed rare gem collector or simply gem enthusiast, you find plenty of rare gems like tephroite to choose from here!

Buy tephroite and other terrific gemstones today!