Euclase is a hard enough gem to be worn safely in jewelry. It may not be terribly exciting to look at (if colorless), but the colored gems are truly beautiful and exceedingly rare over a few carats in size. These gems can be very brilliant. The cleavage makes cutting a bit tricky.
The International Gem Society (IGS) has a list of businesses offering gemstone appraisal services.
|Crystallography||Crystals tabular or prismatic, often well developed.|
|Colors||Colorless, white, pale blue, pale green, violet, dark blue, yellow.|
|Hardness||6.5-7.5. May be variable within a single crystal.|
|Density||2.99-3.10 (colorless = 3.08).|
|Cleavage||Perfect I direction; fracture conchoidal. Brittle.|
|Stone Sizes||Crystals are more commonly found in small sizes, about 1 inch for colorless material. Most euclase, in fact, is colorless, and strongly colored material is very rare. Blue and green gems are scarce over 2-3 carats, with violet being the most unusual. Colorless gems are also rare over 5-6 carats, although stones up to about 20 carats have been cut. Gems reported over 50 carats are museum pieces. Smithsonian Institution (Washington, D.C): 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); Brazilian violet crystals reported that would yield stones up to 10 carats.|
|Luminescence||Feeble or none.|
|Spectral||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.|
|Pleochroism||Zimbabwe dark blue material displays intense pleiochroic colors: azure blue/Prussian blue/ greenish-blue.|
Optics: a = 1.650-1.652; β= 1.655-1.658; γ = 1.671-1.676.
Biaxial (+), 2V= 50°.
Dark blue (Zimbabwe): a = 1.652; β= 1.656; γ= 1.671; Birefringence = 0.019; S.G. = 3.06-3.13.
Occurrence: Euclase is a mineral of granite pegmatites.
Minas Gerais. Brazil: Ouro Preto (fine gem material in good crystals up to a length of about 6 cm); Santana de Encoberto (material with high Birefringence and included crystals of apatite, hematite, futile, and zircon); Boa Vista (cuttable crystals).
Orenburg District, South Urals, USSR: cuttable crystals.
Miami, Zimbabwe: cuttable crystals in shades of intense blue, cobaltian hue, some like fine sapphire.
Morogoro District, Tanzania: Colorado; Ireland; Austria; Norway
Comments: Euclase is a hard enough gem to be worn safely in jewelry. It may not be terribly exciting to look at (if colorless), but the colored gems are truly beautiful and exceedingly rare over a few carats in size. These gems can be very brilliant. The cleavage makes cutting a bit tricky.
Name: From the Greek eu (easy) and klasis (fracture) because of the easy cleavage.