Euclase

Chemistry: Berylium aluminum silicate
Crystal system: Monoclinic; prisms with numerous smooth faces; tabular, well developed.
Color: Transparent; colorless, pale green, light blue, sapphire blue (rare); may be color zoned
Hardness: 7.5
Cleavage: Perfect: 1 direction; Fracture: brittle, conchoidal to uneven.
Specific gravity: 3.10
Refractive index: 1.652 – 1.672; Biaxial positive; 0.02
Luster: Vitreous.
Dispersion: Low.
Dichroism: Weak.
Occurrence: Russia, Africa, Brazil.

Notes
Collector’s stone; name refers to its easy cleavage; may look like aquamarine and green spodumene, but D.R and S.G different; spectra in deep colors: 2 vague bands in blue 468 and 455nm, may also show line in red 705nm; difficult to cut; faceted.