Gemstone Glossary

Euclase

While Euclase's color range is diverse and includes colorless, blue green, blue, yellow, light green and rarely purple, it is typically found in sapphire blue and blue green colors. Sporting a vitreous luster, transparent to translucent crystals, a hardness of 7.5 and a specific gravity of 3.09 - 3.11, Euclase is unfortunately somewhat of an unknown gemstone and it is generally more favored by mineral collectors.


While Euclase forms crystals that occasionally have enough clarity to be cut as gems and with care can be set and worn in jewelry, it is best preserved in collections. The crystals of Euclase are generally prismatic with slanted terminating faces. Euclase's crystals are distinctly monoclinic due to their slanted termination, unlike other monoclinic minerals whose crystals will commonly look like higher symmetry crystals. Strong colored Euclase or nice crystals in larger sizes are quite rare, very attractive and are subsequently much sort after by collectors.

Found in granitic pegmatites with other gem minerals (e.g. topaz and beryl), its crystal form, which could only be confused with barite or celestite, easily identifies Euclase. Furthermore, Euclase is always found in the wrong environment for these sulfate minerals. Additional identification confusion can arise with Topaz, but this stone has a completely different cleavage (i.e. basal compared to the prismatic cleavage in Euclase) and transparent albite, which is softer than Euclase. Interestingly, Euclase that has been weathered from its source rock and transported down stream can be found in alluvial gold deposits.

Euclase has a name that originates from its easy cleavage (i.e. Euclase means easily cleaved) and this is a potential problem for gem cutters who must display great care when working this stone to avoid splitting an unfinished gem. As previously mentioned, this easy cleavage also detracts from the durability of Euclase, greatly limiting its acceptance as a common gemstone. While a skilled gem cutter can work Euclase to its own advantage, another potential negative is the splotchy color distribution of Euclase. Despite Euclase possessing inherent characteristics that limit its appeal, it is a real treasure when a specimen sports well-formed crystals and great color.

Included in its associated minerals are micas, quartz, topaz, beryl, gold, pericline and some feldspar. Euclase can be found in Ouro Preto and other areas within Minas Gerias, Brazil; Kenya; Zimbabwe; Tanzania; Ural Mountains, Russia; Germany and in the famous emerald mines of Columbia.