Euclase
Structure : Monoclinic
Hardness : 7.5
Specific Gravity : 3.09 - 3.1
Refractive index : 1.65 - 1.6
Doubly Refracting (bi-refraction) : 0.019
Chemistry: BeAlSiO4OH, Beryllium Aluminum Silicate Hydroxide.
Class: Silicates
Subclass: Nesosilicates
Uses: Gemstone and as mineral specimens.
Specimens
Euclase is not a well known gemstone, but is more well known by mineral
collectors. It forms well formed crystals that occasionally have enough clarity
to be cut as gems. The sapphire blue and blue green colors of euclase are the
typical colors of the gemstones.
The crystals of euclase are commonly prismatic with slanted termination faces.
Unlike other monoclinic minerals whose crystals will commonly look like higher
symmetry crystals, euclase's crystals are distinctly monoclinic due to the
slanted termination. Nice crystals of euclase are much sought after by
collectors.
Euclase is found in granitic pegmatites with other gem minerals such as topaz
and beryl. It is easily identified by its crystal form which can only be
confused with barite or celestite but is the wrong environment for these sulfate
minerals. Topaz has a completely different cleavage (basal) than euclase
(prismatic). Transparent albite is softer. Euclase weathered out of source rock
and transported down stream can end up being found in placer deposits with gold.
Euclase gets its name from its easy cleavage, euclase simply means easily
cleaved. This is a problem for gem cutters who need to be careful of splitting
an unfinished gem. It also detracts from it durability which limits its
acceptance as a common gemstone. Another negative is its splotchy color
distribution, but a skilled gem cutter can work a stone to its own advantage.
Euclase is a real treasure in well formed crystals and in colorful gemstones.
PHYSICAL CHARACTERISTICS:
Color includes colorless, blue-green, blue, yellow, light green and rarely
purple.
Luster is vitreous.
Transparency: Crystals are transparent to translucent.
Crystal System is monoclinic; 2/m
Crystal Habits include stubby prismatic crystals with non-symmetrical slanted
terminations.
Cleavage is perfect in one direction (prismatic), poor in two other directions.
Fracture is conchoidal.
Hardness is 7.5
Specific Gravity is 3.09 - 3.11 (slightly above average)
Streak is white.
Other Characteristics: Almost always striated lengthwise.
Associated Minerals include micas, quartz, topaz, beryl, gold, pericline and
some feldspars.
Notable Occurrences include Ouro Preto and other areas within Minas Gerias,
Brazil; Kenya; Tanzania; Ural Mountains, Russia; Germany and with emeralds in
the famous mines of Columbia.
Best Field Indicators are crystal habit, good cleavage, striations, hardness and
color.
