Axinite Value, Price, and Jewelry Information

Oval-cut, 3.60-ct axinite, 10.6 x 8.4 x 5.8 mm, purple brown, Pakistan. © ARK Rare Gems. Used with permission.

Axinite

When faceted, the members of the axinite mineral group are usually intensely trichroic, with considerable brilliance and rich brown and purple colors dominating. Although very rare, these gems could make magnificent jewelry stones.

Axinite Value

The International Gem Society (IGS) has a list of businesses offering gemstone appraisal services.

Axinite Value via Gem Price Guide

Accompanying value information:
Faceted 1 to 5 carats
to /ct

Axinite Information

Data Value
Name Axinite
Varieties Ferro-axinite, Magnesio-axinite, Manganaxinite
Colors Violet-brown, colorless, reddish purple, pink, orange, yellowish (Mn), greenish, pale violet to reddish (Mn), violetish blue, blue (Mg).
Crystallography Triclinic. Distinctive wedge-shaped crystals; also tabular
Refractive Index 1.656-1.704
Luster Vitreous.
Hardness 6.5 - 7, variable with direction
Wearability Very Good
Fracture Uneven to conchoidal
Specific Gravity 3.26-3.36; magnesioaxinite = 3.18
Birefringence 0.010-0.012
Cleavage Good 1 direction
Dispersion 0.018-0.020 (Large)
Heat Sensitivity Slight
Luminescence Red in SW (Franklin, New Jersey). Dull red in SW, orange-red in LW (Tanzania: magnesioaxinite).
Luminescence Present Yes
Luminescence Type Fluorescent, UV-Long, UV-Short
Enhancements None
Transparency Translucent to transparent.
Absorption Spectrum Narrow line at 5120, broad lines at 4920 and 4660, also at 4150. Sometimes lines visible at 5320, 4440, and 4150 (latter may be strong).
Phenomena Color change (Very Rare).
Formula

(Ca, Mn, Fe, Mg)3Al2BSi4O15(OH).

  • +Mg = magnesioaxinite
  • If Fe > Mn = ferroaxinite
  • If Mn > Fe = manganaxinite
  • If Mn > Fe and Ca <1.5 = tinzenite
Pleochroism

Intense in all colored varieties: cinnamon brown/violet-blue/olive green, yellow, or colorless.

  • Luning, Nevada material: pale brown to colorless/deep brown/ brownish red.
  • Magnesioaxinite: pale blue/pale violet/pale gray.
  • Manganaxinite: blue/brown/purple.
  • Tinzenite: pale brown/violet/colorless to yellowish.
  • Sri Lanka material: reddish brown/dark violet/ colorless to yellowish.
Optics

α = 1.674 – 1.693; β = 1.681 – 1.701; γ = 1.684 – 1.704.

Magnesioaxinite: α = 1.656; β = 1.660; γ = 1.668

Biaxial (-), 2V = 63-80° or more. However, may turn (+) if high in Mg.

 

Optic Sign Biaxial +, Biaxial -
Etymology

From the Greek axine for “axe,” alluding to the common wedge shape of its crystals. Ferroaxinite, magnesioaxinite, and manganaxinite refer to the chemical composition of these varieties. Tinzenite refers to the type locality of this variety, Tinzen, Switzerland.

Occurrence

Axinite is found in areas of contact metamorphism and metasomatism.

Inclusions

Usually included.

axinite - Baja California

Axinite: Baja California, Mexico (~ 2.0 cut, rough 1½ inches long). Photo © Joel E. Arem, PhD, FGA. Used with permission.

Comments

Axinites form a mineral group, which includes iron (Fe) dominant ferroaxinite, magnesium (Mg) dominant magnesioaxinite, and manganese (Mn) dominant manganaxinite. Tinzenite is an intermediate member between ferroaxinite and manganaxinite.

Most gem-quality axinites are ferroaxinites, but you will likely encounter specimens called simply “axinites.” However, specific gems should ideally be referred to by their composition-specific names or with designations such as “axinite-(Fe).”

manganaxinite - axinite crystals, Arizona

Greenish manganaxinite crystals on acicular johannsenite crystals. Field of view 7 mm. Iron Cap Mine, Landsman Camp (Landsman group), Aravaipa, Santa Teresa Mts, Aravaipa District, Graham County, Arizona. Photo and specimen Leon Hupperichs. Licensed under CC By-SA 3.0.

These strongly pleochroic gems can show three colors, depending on the viewing angle, and can have significant brilliance, too. (See the “Pleochroism” section in the Information Table above). With a hardness of 6.5 to 7, axinites of all varieties have “Very Good” wearability grades. This means they can withstand the rigors of use in most jewelry settings. However, these stones have anisotropic hardness. It may vary within a single specimen depending on the gem’s orientation. In addition, they have somewhat brittle tenacity.

Axinites are almost never completely free of clarity flaws, such as feathers and veils. Nevertheless, because of their rarity, these exquisite gems would still command the interest of both gem collectors and jewelry enthusiasts.

Most gem-quality specimens of the axinite group are iron-dominant ferroaxinites, like the rough and cut set shown here. 2.2 x 1.7 x 0.3 cm (crystal), 1.95-ct (gem), Puiva, Saranpaul, Tyumenskaya Oblast’, Prepolar Ural, Russia. © Rob Lavinsky, www.iRocks.com. Used with permission.

Identifying Characteristics

Axinites are both piezoelectric and pyroelectric. They generate an electrical charge under physical pressure and when heated, respectively.

Although typically biaxial negative, an axinite’s optic character may become biaxial positive as its Mg content increases.

Unusual violetish blue and reddish purple color zoning has been documented in ferroaxinites from Pakistan.

Rare magnesioaxinites have demonstrated a slight color change effect. Specimens from Tanzania have shown a pink color under incandescent light and a blue color under fluorescent light. Other changes have also been noted.

This faceted magnesioaxinite shows a very slight color change, from violetish purple in daylight to pink in incandescent light. Diamond step cut, 0.53 cts, 7.1 x 5.7 mm, Merelani, Tanzania. © The Gem Trader. Used with permission.

Axinite and another rare gemstone, andalusite, have overlapping ranges of body and trichroic colors as well as hardness. However, axinite’s refractive index (RI) range and specific gravity (SG) range exceed those of andalusite.

pear-cut axinite - Pakistan

This pear-cut axinite from Pakistan shows this gem’s strong pleochroism. When you view the gem through the crown, you’ll see a honey brown color. When you view the gem through the pavilion, however, you’ll see a lilac hue. 3.27 cts, 12.5 x 8.5 mm. © Rob Lavinsky, www.iRocks.com. Used with permission.

Synthetics

No known synthetic axinites.

Enhancements

No known gemstone treatments.

tinzenite crystals - axinite, Italy

Bright orange tinzenites on clear quartz crystals, 3.2 x 2.2 x 1.5 cm, Molinello Mine, Graveglia Valley, Ne, Genova Province, Liguria, Italy. © Rob Lavinsky, www.iRocks.com. Used with permission.

Sources

Axinites occur in many localities across the globe, but gem-quality material is rare. Notable sources include the following:

axinite crystals - Japan

Clove brown axinite crystals, 2.5 x 2.0 x 1.6 cm. Obira mine, Ono-gun, Oita prefecture, Kyushu Region, Japan. © Rob Lavinsky, www.iRocks.com. Used with permission.

Stone Sizes

Axinites with clean clarity over 5 carats are difficult to find and worthy of museum display. Faceted specimens of any type over 10 carats are rare. Material from Baja California will yield gems to about 25 carats. However, if clean, these stones will cut less than 5 carats.

Care

Although resistant to scratching due to their hardness, axinites have good cleavage and brittle tenacity. Avoid jewelry settings where these gems may receive blows.

Although axinites have very good wearability, their inclusions may pose risks if these gems are cleaned in mechanical systems. Have a gemologist examine them, identify any inclusions, and recommend a cleaning method. Since axinites also have some heat sensitivity, avoid boiling or steam cleaning. A soft brush, mild detergent, and warm water can serve as a safe alternative. Consult our gemstone jewelry cleaning guide for more recommendations.

faceted axinite - Brazil

Faceted axinite, 1.02 cts, Brazil. Photo by DonGuennie. Licensed under CC By-SA 4.0.

by Joel E. Arem, Ph.D., FGA, Donald Clark, CSM IMG, International Gem Society

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