The Beryl Types:
Composition: Beryllium Aluminum Silicate
Crystal System: hexagonal; 6/m 2/m 2/m
Hardness: 7.5 - 8
Specific Gravity: 2.6 - 2.9
Refractive Index: 1.5 - 1.6
Cleavage: poor basal
Color: bright green, blue, greenish-blue,
yellow, red, pink, white, colorless.
Transparency: Crystals are transparent to translucent
Associated Minerals: calcite, euclase,
some feldspars, micas, quartz and tourmalines.
Beryllium aluminum silicate (14.0% BeO, 19.0% A1203,
67.0% Si02 sodium, lithium, and caesium may replace
part of the beryllium, thus reducing the BeO content and lowering its
value as an ore).
The pegmatitic occurrence and six-sided outline are very characteristic.
Only likely to be con- fused with Apatite (which is much softer and
is fluorescent and soluble in acid), with white, massive topaz ( infusible),
and with quartz. Beryl is commonly used as a gemstone. Beryl
is colorless in pure form, but different impurities give beryl many
varied colors. It's refractive index is low so Beryl only has average
fire and brilliance. However varied colors make the Beryl gems quite
appalling. Emerald is the green variety and Aquamarine is the blue variety
of beryl. Other colors of beryl are also used as gemstones but are not
as well known. The greenish-yellow variety is called Heliodor. The pink
variety is called Morganite. The colorless variety is called Goshenite.
The name beryl is used for the red and golden varieties, which are simply
called red beryl and golden beryl.
As a rule Beryl is a mineral of ancient deeply buried rocks.
So it is almost exclusively a pegmatite mineral. Can form in high-temperature
veins and pockets by beryllium-bearing
gases or very hot solutions.
Crystal Habits typically include the hexagonal prism with pincoid terminations.
The terminations are often modified by many different pyramidal faces
which can sometimes produce a rounded termination. The crystal face
shows very fine striations (ridges) along its length. Rarely in tabular
crystals, with the pink caesium beryls more likely to have this flat
habit. Also massive and embedded as grains or columnar masses. Individual
crystals can become very large. Single crystals have been found as large
as 25 tons.
When heated with athe blow pipe beryl glows whitely, does
not decrepitate too violently to re- main intact in the flame, and fuses
with great difficulty to a white glass. Insoluble in the common acids.
There are many localities in New England, with
well formed crystals in quartz and feldspar. North Carolina is also
a source of common beryl, and the Emerald. Tabular beryl crystals have
been found in some abundance in New Mexico at Dixon. Large crystals
are found in the Black Hills of South Dakota. In San Diego County, gemstone
quality aquamarine and morganite have been found in pegmatite in Mesa
Grande, Pala, and Ramona. Emeralds are found in veins in a black limestone
at Muso, and in a pegmatite at Chivor, Colombia. Biotite schists bordering
a pegmatite are the source of the emeralds in Takowaja, Russia, accompanied
there by chrysoberyl and phenakite. Large crys- tals with fine morganites
come from Madagascar. Brazil is the chief source of aquamarine, and
crystals weighing several hundred pounds have been recovered from stream
beds, principally in Minas Gerais.
Beryl is the chief ore of beryllium. Transparent varieties
have gem value
FACTS & HISTORY:
It is suspected that the word brilliance is probably derived from
the ancient Greek word for beryl, berullos, which means crystal.
(also known as bixbite)
is the rarest form of beryl. Red Beryl was first noted in Utah in 1905,
in the Thomas Range in Juab County, Utah. In the late 1950's the only
crystals suitable for faceting were found in the Wah Wah Mountains,
near Beaver, Utah. Red Beryl crystals can be redish to redish orange
to a purplish red. Red Beryl occurs as hexagonal crystals which is typical
of beryls. The specific gravity is 2.66-2.7 and the refractive index
is 1.564-1.574. It's primary chemical composition is Be3Al2SiO3,
but there are traces of many other elements. Red Beryl is thought to
have formed as a vapor phase reaction in the rhyolite magma. Normaly
rhyolite lacks gem minerals and beryl is even more uncommon. So the
presence of Red Beryl suggests some unusual conditions for gemstone
formation. One of the largest crystal ever recovered was 14mm x 34mm
and weighed approximately 54 carats. The average faceted gemstone is
.15 carats and the largest faceted gemstone to date weighed 8.0 carats.