Euclase Value, Price, and Jewelry Information


oval-cut euclase - Brazil
Oval-cut, pale yellow euclase, 4.26 cts, 12.8 x 9.8 x 5.2 mm, Ouro Preto, Brazil. © ARK Rare Gems. Used with permission.

Although hard enough to be worn safely in jewelry, euclase in beautiful colors is rare over a few carats. It’s also a difficult gem to facet.

Euclase Value

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

Euclase Information

DataValue
NameEuclase
Crystallography Monoclinic, crystals tabular or prismatic, often well developed.
Refractive Index 1.650-1.676
Colors Colorless, white, pale blue, pale green, violet, dark blue, yellow. May show blue/colorless or light blue/dark blue color zoning.
Luster Vitreous.
Fracture Conchoidal
Hardness 6.5-7.5. May be variable within a single crystal.
Specific Gravity 2.99-3.10. Colorless = 3.08; dark blue (Zimbabwe) = 3.06-3.13.
Birefringence 0.019-0.024
Cleavage Perfect 1 direction
Dispersion 0.016
Luminescence Feeble or none.
Enhancements Radiation can turn colorless euclase blue or green.
Transparency Transparent to translucent.
Absorption Spectrum There are two vague bands at 4680 and 4550; if Cr is present, it may display a characteristic spectrum in the red with a doublet at 7050.
FormulaBeAISiO4(OH)
Pleochroism Light colored material may display: bluish gray/light blue/colorless; yellow-green/blue-green/colorless; white-green/yellow-green/blue-green. Zimbabwe dark blue material displays intense pleiochroic colors: azure blue/Prussian blue/greenish-blue. Chromium-colored material may display purple/blue-green/colorless.
Optics a = 1.650-1.652; β = 1.655-1.658; γ = 1.671-1.676. Biaxial (+), 2= 50°. Dark blue material (Zimbabwe): a = 1.652; β = 1.656; γ = 1.671; Birefringence = 0.019.
EtymologyFrom the Greek eu for “easy” and klasis for “fracture,” because of its easy cleavage.
OccurrenceEuclase is a mineral of granite pegmatites.
4 faceted euclase gems - Brazil
Euclase: Brazil (ca 0.3 to 1.3). Photo © Joel E. Arem, PhD, FGA. Used with permission.

Comments

Colorless euclase may not look terribly exciting, but faceted pieces can have exceptional brilliance. Strongly colored euclases in blue or green are prized by collectors of rare gems. Violet is the rarest and most desired color.

With hardness ranging from 6.5 to 7.5, euclases would make good jewelry stones, but they present some challenges for faceters. Their perfect cleavage in one direction makes cutting a bit tricky. Jewelers would also need to set this stone with care, especially in a ring, to avoid placing stress on its cleavage plane.

blue euclase crystals - Zimbabwe
Gemmy, blue euclases, 2.7 x 2.2 x 1.6 cm, Karoi District, Mashonaland West, Zimbabwe. © Rob Lavinsky, www.iRocks.com. Used with permission.

Identifying Characteristics

Euclases may have variable hardness even within the same crystal.

Most euclases receive what color they have from traces of iron. However, some euclases from Colombia receive their greenish blue color from traces of chromium. These stones appear red under a Chelsea filter.

light green euclase crystals - Colombia
Set of euclases, light grass-green with hints of blue, 1.5 x 0.9 x 0.5 cm, Gachala, Guavio-Guateque Mining District, Boyaca Department, Colombia. © Rob Lavinsky, www.iRocks.com. Used with permission.

Synthetics

No known synthetics.

Be aware that some aquamarines have been misrepresented as much rarer light blue or green euclases to sell for more money. Although euclase can form geologically from the decomposition of beryl and is often found with beryl, they’re distinct mineral species. They have different optical and physical properties.

Enhancements

Radiation treatments can turn colorless euclases green or blue.

Sources

Brazil produces most cuttable, gem-quality euclases. In Minas Gerais, Ouro Preto yields fine gem material in good crystals up to a length of about 6 cm. Santana de Encoberto yields material with high birefringence and included crystals of apatite, hematite, rutile, and zirconBoa Vista also yields cuttable crystals.

bi-color euclase - Brazil
Bi-color colorless/blue euclase, 0.45 cts, 5 x 4 mm, emerald cut, Brazil. © The Gem Trader. Used with permission.

Miami, Zimbabwe produces cuttable crystals in shades of intense, cobaltian blue hue, some look like fine sapphires.

Other notable gem-quality sources include the following:

  • Orenburg District, South Urals, Russia: cuttable crystals.
  • Austria; Colombia; Ireland; Myanmar; Norway; Morogoro District, Tanzania; Colorado, United States.
oval-cut euclase - Russia
Oval-cut, pale yellow euclase, 3.60 cts, 11.2 x 8.8 x 5.7 mm, Russia. © ARK Rare Gems. Used with permission.

Stone Sizes

Crystals most commonly occur in small sizes, about 1” for colorless material. Most euclases are, in fact, colorless. Strongly colored material is very rare. Blue and green gems are scarce over 2-3 carats. Some Brazilian violet crystals reportedly could yield stones up to 10 carats.

Colorless gems over 5-6 carats are also rare, although stones up to about 20 carats have been cut. Gems reported over 50 carats are museum pieces.

  • Smithsonian Institution (Washington, DC): 144 (lime green, Brazil); 48.7 (green): 12.5 green, Brazil; 8.9 (yellow, Brazil); 3.7 (blue-green, Brazil).
  • Devonian Group (Calgary, Alberta, Canada): 15.45 (colorless, Brazil): 14.0 (mint green, Brazil).
  • Private Collection: 18.29 (blue-green oval, Brazil); 7.43 (blue, Brazil).

Care

Due to their perfect cleavage, don’t clean euclases with mechanical systems. Use only warm water, mild detergent, and a soft brush. Use protective settings for rings and make sure you discuss with your jeweler how best to set any euclases.

For more cleaning recommendations, consult our gemstone jewelry care guide.

2 faceted euclase gems - Brazil
Euclase: Brazil (5.49, 1.34). Photo © Joel E. Arem, PhD, FGA. Used with permission.