Triphylite (or tryphylite) is one of the world's rarest gems. The IGS had the extraordinary privilege of examining a discovery of facetable material from Brazil that showed previously unknown characteristics.
Triphylite values vary considerably, due to rarity and demand. Some have sold for $250 per carat. At auction, demand has driven prices as high as $4,500 per carat.
The International Gem Society (IGS) has a list of businesses offering gemstone appraisal services.
|Crystallography||Orthorhombic; crystals prismatic, often with rounded faces, but very rare: usually massive, cleavable, and compact.|
|Colors||Greenish gray, bluish gray; alters to brownish or blackish hues. (Lithiophilite is clove brown, yellowish brown, honey yellow, or salmon).|
|Luster||Vitreous; resinous to sub resinous.|
|Fracture||Sub-conchoidal to uneven.|
|Specific Gravity||3.42. (See "Identifying Characteristics" below).|
|Cleavage||Perfect 1 direction.|
|Spectral||See "Comments" below.|
|Transparency||Transparent to translucent.|
|Formula||Li(Fe+2, Mn+2)PO4 + Mg. Series to lithiophilite.|
|Pleochroism||Absent or very weak; some lithiophilite may show deep pink/pale greenish yellow/pale pink. See “Comments” below.|
|Optics||a = 1.689-1.694; β = 1.689-1.695; γ = 1.695-1.702. Biaxial (+). See “Identifying Characteristics” below.|
|Etymology||From the Greek words tri and phylon, meaning “family of three,” probably alluding to the presence of three cations (positively charged atoms) in its formula: lithium, iron, and manganese.|
|Occurrence||As a primary mineral in granitic pegmatites, often altered to a wide array of secondary phosphates.|
As any long-term student of gemology knows, the reported properties of gems expand over time. Textbooks written in the 1950s show a narrower range of properties than those written in the 1990s and 2000s. The simple reason is that gemologists have examined more gems. Thus, more information becomes available.
With gems as rare as triphylite, gemologists have examined very few specimens ever. In addition, this phosphate mineral forms a solid solution series with lithiophilite. As a result, previously unobserved blends can appear. Lithiophilite has a chemical formula nearly identical to triphylite: Li(Mn+2, Fe+2)PO4. It differs by being rich in manganese instead of iron. Due to this lower iron content, lithiophilite is slightly less dense. Its colors run from pinkish to greenish brown, while triphylite’s color is usually a gray shade of blue or green.
Triphylite is a primary phosphate mineral. It alters easily into other phosphate minerals, especially manganese phosphates. Secondary phosphate minerals include: dickinsonite, eosphorite, fairfieldite, fillowite, heterosite, hureaulite, phosphoferrite, purpurite, reddingite, salmonsite, sicklerite, stewartite, strengite, triploidite, vivianite, and wolfeite.
New Facetable Triphylites from Brazil
The new discovery clearly shows the blend, being clove brown and grayish green. Previously studied examples of this gem were just melee size and had very little pleochroism. The newly discovered gems go up to two carats and show beautiful orangish/brown and green pleochroism, similar to andalusite.
Below is a summary of their properties.
- Refractive Index: 1.680 – 1.695
- Birefringence: 0.011 – 0.015
- Color: Clove brown and grayish green.
- Cleavage: Perfect one direction (basal) and imperfect in two directions (prismatic). All cleavages are at right angles to each other.
- Absorption Spectrum: Strong line at 485 and strong to weak line at 460.
- Pleochroism: orangish/brown and green.
You may sometimes observe triphylites with optic character biaxial (-). Depending on the Fe: Mn ratio, you may observe uniaxial interference figures. Refractive indices increase with Fe content but may substantially decrease if Mg substitutes for (Fe, Mn).
Pure Fe end of the triphylite-lithiophilite series = 3.58. The pure Mn end (lithiophilite) = 3.34. The halfway point (Fe: Mn = 1:1) = 3.52. Density isn’t linear with Fe: Mn ratio.
Minas Gerais, Brazil has produced facetable material. Other notable gem-quality sources include:
- United States: Pala, California; Maine; Massachusetts; New Hampshire (excellent crystals at Chandler’s Mill, Palermo, Grafton Center, North Groton); Black Hills, South Dakota (as enormous crystals up to 6 feet long).
- Finland; France; Germany; Sweden.
Triphylites don’t usually form in distinct crystals. Most crystals appear as compact masses, embedded in other stones, or as inter-grown crystal clumps. Facetable material is very rare. Most gem-quality material is best suited for cabbing.
Conceivably, lapidaries could cut large stones from some of the immense crystals found in South Dakota. However, this material is usually opaque or altered. The Brazilian material has yielded tiny, brown, cut stones.
Triphylites could have more surprises in store for gem collectors. New sources could yield cuttable crystals at any time.
With perfect cleavage and mid-range hardness (4-5), these gems would require great care as jewelry stones. Make sure they have protective settings and avoid ring use. You’re more likely to encounter these rare gems, if at all, in gem collections than jewelry collections.
Store these gems separately from other harder stones to avoid contact scratches. For cleaning, use a soft brush, mild detergent, and warm water. Consult our Gemstone Jewelry Cleaning Guide for more recommendations.