THE MINERAL CHRYSOBERYL | Chrysoberyl Crystal from ceylon

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Chrysoberyl is an uncommon mineral, and the color-changing variety Alexandrite is quite rare and highly valued. The nature of Alexandrite is very unique. If viewed in sunlight, its color is dark yellow-green to greenish-blue, and if viewed in incandescent light, its color changes strawberry-red to dark pink. This phenomenon is caused by the presence of certain impurities, and only occurs in Chrysoberyl from a few scattered findings.

Chrysoberyl can exhibit a floating light reflection that moves as when a polished gem is rotated. This effect is known as cymophane effect. If a Chrysoberyl exhibits a thin narrow band of reflecting light across its length which slightly moves when a polished gem is rotated, the effect is known as a cat's eye effect. Cat's eye and cymophane effects are caused by microscopic, parallel, needlelike inclusions that cause the light to reflect distinctly within a stone. Both Cymophane and Cat's Eye are variety names used to described Chrysoberyl with these effects. Other minerals and gemstones may also exhibit cymophane or cat's eye effect, but Cymophane and Cat's Eye when used alone are only describing the Chrysoberyl type. For example, Quartz that exhibits cat's eye is known as Cat's Eye Quartz (or Quartz Cat's Eye), whereas Chrysoberyl Cat's Eye is known simply as Cat's Eye. Alexandrite may also occur in Cat's Eye or Cymophane forms, but this is extremely rare.

For additional information, see the gemstone section on Chrysoberyl, Alexandrite, and Cat's Eye.

Chemical Formula BeAl2O4
Composition Beryllium aluminum oxide, commonly with small amounts of iron and chromium
Color Yellow, orange-yellow, yellow-green, dark to light green, brownish-green, bluish-green, brown, gray. The variety Alexandrite becomes reddish in artificial light.
Streak White
Hardness 8.5
Crystal System Orthorhombic
3D Crystal Atlas
(Click for animated model)
V-shaped Contact Twin
Repeated Penetration Sixling
Non-twinned Tabular
Crystal Forms
and Aggregates As thick tabular crystals, as well as long, prismatic crystals. Crystals are often distinctively twinned, either in v-shaped repeated twins or in snowflake-shaped trillings where three individual crystals join to form a unique hexagonal pattern. Crystals are frequently striated, and may be smooth on the edges or rounded due to alluvial action.
Transparency Transparent to translucent
Specific Gravity 3.5 - 3.8
Luster Vitreous
Cleavage 1,1 ; 3,2. Commonly parts along twinned crystals.
Fracture Conchoidal to uneven
Tenacity Brittle
Other ID Marks 1) Some specimens fluoresce red or green in shortwave ultraviolet light.
2) The variety Alexandrite changes color in incandescent light.
Complex Tests Insoluble in acids
In Group Oxides; Multiple Oxides
Striking Features High hardness, high specific gravity, and crystal forms.
Environment In granite pegmatites and regional metamorphic rocks.
Rock Type Igneous, Metamorphic
Popularity (1-4) 1
Prevalence (1-3) 3
Demand (1-3) 1