 |
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 | 8½ | ||
|
Crystal Forms and Aggregates |
(Orthorhombic) Crystals occur in thick tabular crystals, as well as long, prismatic crystals. Crystals may twin, where three individual crystals join to form a snowflake-shaped trilling. Crystals are frequently striated. | ||
|
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) The variety Alexandrite has a different
color in artificial and natural light 2) Some specimens fluoresce red or green in shortwave ultraviolet light |
||
|
Varieties |  Alexandrite - Variety that
exhibits a different color in artificial and natural
light. Cat's Eye - Polished
Chrysoberyl exhibiting a cat's eye effect (reflects a long thin wave of
light across the specimen). Chrysolite
- Incorrect name occasionally used to describe yellow,
transparent Chrysoberyl. Cymophane
- Polished Chrysoberyl exhibiting a floating light
reflection (see cymophane effect) Precious
Cat's Eye or Precious Catseye -
Synonym of Cat's Eye |
||
|
In Group | Oxides ; Multiple Oxides | ||
|
All About | Chrysoberyl is a rare gemstone. The
attractive properties of Alexandrite and Chrysoberyl are
responsible for their high demand. Other transparent
Chrysoberyl does not have the appeal of Beryl or other precious gemstones,
because it lacks luster and fire, although the
yellow-green variety commends a high value. The nature of Alexandrite is unique. If viewed in sunlight, its color is dark yellow-green to greenish-blue. If viewed in artificial light, its color is strawberry-red. This phenomenon is caused by the presence of certain impurities, and adds attractiveness to this stone. If Chrysoberyl exhibits a floating light reflection that moves as the gem is rotated, it is known as Cymophane. The effect is known as "cymophane effect". If a stone exhibits a thin narrow band across its length of reflecting light which slightly moves when the stone is rotated, it is a Cat's Eye, which produces an effect known as cat's eye effect. The cat's eye and cymophane effects are caused by microscopic, parallel, needlelike inclusions. If the term "Cat's Eye" is used singularly (without a preceding mineral name), it describes Chrysoberyl exhibiting cat's eye effect. If another mineral exhibits cat's eye effect, the name of the mineral is placed together with the term "Cat's Eye". For example, Quartz that exhibits cat's eye is known as Cat's Eye Quartz or Quartz Cat's Eye. Alexandrite may occur in Cat's Eye or Cymophane forms, but it is extremely rare. |
||
|
Uses | Chrysoberyl makes a fine gemstone. The
Alexandrite and Cat's Eye varieties are very expensive.
Clear yellow and green stones are also valuable
gemstones, but are less than Alexandrite and Cat's Eye. Chrysoberyl is a minor ore of beryllium. Also see the gemstone section on Chrysoberyl |
||
|
Striking Features | High hardness, high specific gravity, crystal shape | ||
|
Complex Tests | Insoluble in acids | ||
|
Popularity (1-4) | 1 | ||
|
Prevalence (1-3) | 3 | ||
|
Demand (1-3) | 1 | ||
|
Distinguishing Similar Minerals |
Beryl - different crystal system,
somewhat softer (7½ - 8) Topaz - very hard to distinguish without complex tests, although Chrysoberyl is generally paler in color |
||
|
Commonly Occurs With |
Beryl, Tourmaline, Microcline, Albite, Quartz, Garnet | ||
|
Noteworthy Localities |
Chrysoberyl is a very rare mineral, and its
occurrences are limited. Large deposits exist in the Ural
Mountains in Russia, where much Alexandrite has also been
found. The best material in the Urals and perhaps in the
world occurs near Sverdlovsk. The provinces of Minas
Gerais and Bahia in Brazil have scattered localities. It
also occurs as waterworn pebbles in Mogok and Pegu,
Myanmar (Burma), and in Sri Lanka, particularly in
Ratnapura. It is also found in small deposits in India,
Tanzania, Zimbabwe, and Madagascar. In the U.S., it occurs in the Gillette Quarry, Haddam, Middlesex Co., Connecticut; Topsham, Sagadahoc Co., Maine; and Greenfield, Saratoga Co., New York. Fairly large crystals occur near Golden, Jefferson Co., Colorado. |
||
|
Picture Icon Links |
|
||
|
Picture Links | 1. Chrysoberyl Cat's Eye |
