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Heliodor (Beryl) Mineral Facts:
Chemical Formula: Be2Al22(SiO3)6
A trace of water is included.
Colors:
Heliodor
is the
marketing name for the yellow to golden variety of the gemstone beryl,
but is not nearly as popular or common as many of the other color forms. It is colored by ferric
iron. Its streak is white.
Hardness:
7.5 to 8.0
Hardness varies somewhat depending
on formation and impurities.
Density: 2.6
to 2.8
Cleavage:
Beryl's
cleavage is very imperfect but there is frequently a parting parallel to
the base.
Crystallography: Hexagonal
Strong
prismatic habit. The
usual form is in sharp and,
in some cases, very large columnar crystals with a distinct hexagonal
habit. Heliodor
is normally found in crystals elongated on the "C" axis.
Crystals are frequently vertically striated and grooved. Forms usually
present consist only of prism of first order and base. Crystals can be
of considerable size with rough faces.
Luster:.
Beryl has a glassy
luster. It is transparent or translucent. Heliodor is the name
given to the yellow-golden version of this transparent stone. Used as a gem or as a
collectors stone.
Optics:
(Refractive Index):
w= 1.5740, e= 1.5690
Pleochroism
is noticeable in green (emerald) and blue (aquamarine) crystals, but not
as much in this yellow variety.
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Composition,
Structure and Associated Minerals:
Beryl is a frequent constituent
of coarse-grained granites. It is important as a gem material, and is
particularly interesting because of the many physical investigations that
have been made with the aid of its crystals. Although the mineral is
essentially a beryllium alumino-metasilicate, it usually contains also a
little Fe2O3
and MgO, in many
cases small quantities of the alkalies, and in some
cases also caesium. The mineral occurs as an accessory constituent in
pegmatites and granites, in crystalline schists, especially mica schists and
gneisses, in ore veins and sometimes in clay slates and bituminous
limestones.
Uses. The impure varieties are used
as an important ore of the Space-age metal Beryllium. The transparent
varieties are utilized as gems, under the following names:
Emerald is a deep green variety, the color is
due to Chromium or Vanadium.
Aquamarine, a blue-green variety, colored by
iron.
Golden beryl, a golden yellow-colored variety,
Morganite, a pink, high cesium variety, and
Goshenite or White beryl, a colorless variety.
Identification and Diagnostics
Beryl
whitens and fuses
with difficulty at 5-5.5 to an enamel. Yields a little water on intense
ignition. Insoluble in acids. Recognized usually by its hexagonal crystals,
its hardness, color, etc. Beryl is distinguished from apatite, which it much
resembles, by its greater hardness.
Occurrence,
Localities and Origins (Heliodor):
Beryl of the
yellow to golden heliodor color is much less known than other beryls like
aquamarine and emerald. It has been
found in gem quality in Brazil, Siberia, East Africa, Afghanistan and in small amounts
from many other countries. Brazil, however, is by far the most important
producer, and has been the most important producer for more than a century.
Many mines in the Brazilian state of Minas Gerias produce fine heliodor
crystals. In the United States a few heliodor gems have been found in California. The color
of heliodor is stable. The name comes from the Greek words
for sun (helios)
and gift (doron).
Attractive crystals are popular with mineral collectors.
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Mineral Collectors Information Page |
Heliodor Beryl Crystal, Brazil |
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