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Chrysoberyl Mineral Facts:

Chemical Formula: BeAl₂O₄

Colors: Chrysoberyl can be colorless or of some light shade of green, yellow, or brown. Alexandrite is the photochroic form changing from green to red-purple form that is green by daylight and red by incandescent light. It is colored by chromium.   Chrysoberyl's streak is white.

Hardness: 8.5

Density: 3.6

Cleavage: Indistinct Prismatic cleavage in three directions.

Crystallography: Orthorhombic
Crystals usually tabular parallel to macropinacoid, which face is vertically striated. Commonly twinned, often in pseudohexagonal forms.

Luster:.  Chrysoberyl has a glassy luster. It is transparent or translucent. 

Optics: (Refractive Index):  a= 1.7470, b= 1.7484, y= 1.7565

Composition, Structure and Associated Minerals:
Chrysoberyl is a beryllium aluminate, the composition of which is analogous to that of the spinels. It is rarely pure. and analyses of nearly all specimens show the presence also of iron and magnesium.

The main use of chrysoberyl is as a gem and collectors stone but it not commonly found in most jewelry stores because of its rarity. The ordinary yellowish green stones are comparatively inexpensive, but rare. Alexandrite is much more expensive, and brings more than $1000  for a fine quality one-carat stone. The cat's-eye variety may also sell for very high values in fine quality stones.

Identification and Diagnostics
Chrysoberyl is characterized by its extreme hardness, its yellowish to emerald-green color and its unusually twined crystals. Before the blowpipe the mineral is infusible. It yields the Al reaction with Co(NO3)2, but otherwise is only slightly affected by the flame. It is insoluble in acids. It most closely resembles the beryllium silicate, beryl, in appearance, but is easily distinguished from this by its hardness and crystallization.  

Occurrence, Localities and Origins:
Chrysoberyl is found principally in granitic rocks and crystalline mica  schists and as placer grains in the sands which are produced by the erosion of these rocks. In its original position, the mineral results from the last volatile fraction of the magma that contains materials which are not easily incorporated into normal rock forming minerals. Chrysoberyl is a rare mineral. Found in the alluvial gem deposits of Brazil and Ceylon; the alexandrite variety comes from the Ural Mountains, Africa and Brazil. A fine deposit of  Alexandrite was found in Brazil in the 1980s. In the United States it has been found at Norway and Stoneham, Maine; Haddam, Connecticut; and in North Carolina.

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