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Hiddenite
Mineral Facts:
Chemical Formula: LiAlSi2O6
Hiddenite is a green
color variety of spodumene which is used as a gemstone. Spodumene
is a
member of the pyroxene mineral
family.
Colors:
white, gray, green or yellowish
green, blue, violet to amethystine.
The Hiddenite variety is green, the pink to violet to purple or even
blue varieties are named Kunzite. The element Chromium present as a
coloring agent is thought to give Hiddenite its color. Both the gem
varieties kunzite and hiddenite are
noted for their strong pleochroism, they are darker looking down the C
axis.
Hardness:
6.5 to 7
Density: 3.18
Cleavage:
Two
planes yielding a perfect prismatic cleavage.
Crystallography: Monoclinic
Most crystals
are striated vertically. Twins are fairly common. Although crystals are
common the mineral also frequently occurs as platy or scaly aggregates.
Luster:.
Vitreous luster which
can be pearly on cleavage surfaces.
Optics:
(Refractive Index): = a =1.651,
b=1.669, y=1.677.
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Hiddenite Chrome Spodumene, Adams Farm,
North Carolina, USA |
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Composition, Structure and
Associated Minerals:
Spodumene
occurs in granites, pegmatites and crystalline schists, where it was formed
by pneumatolytic processes. A comparatively rare species, but found
occasionally in very large crystals in certain pegmatite dikes. At the Etta
Mine, Black Hills, South Dakota, are many 30 ft. long and 3-4 ft. in
diameter. One measured 47 ft. in length. At the Etta tin pegmatite in
Pennington County, South Dakota, it is often associated with
cassiterite. As a constituent of Lithium rich pegmatites in
California it often occurs associated with lepidolite and
tourmaline, and it has been mined for its lithium content. The
best-known gem varieties are Hiddenite and kunzite. There is, however, a
yellow transparent variety of spodumene; specimens of this variety occur
associated with
chrysoberyl in Brazil, and are sometimes sold as chrysoberyl, from
which, however, they can readily be distinguished by their inferior hardness
and lower specific gravity. Spodumene alters readily to albite, muscovite,
eucryptite, or mixtures of these minerals.
Identification
and Diagnostics
Before the blowpipe
spodumene
swells up and
throws out fine
branches at first,
eventually
fusing
to a
clear,
colorless glass, at
the same time imparting a crimson color to the flame (test for lithium). It
is unattacked by ordinary acids. It melts at about 1325. Its powder reacts
alkaline.
It is recognized by its cleavage, positive test for lithium and associated
minerals.
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Green Spodumene, Brazil |
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Localities
Hiddenite is the clear,
transparent variety of spodumene ranging in color from yellow-green to deep
emerald green tones. It occurs at Stony Point, Alexander Co., North
Carolina, in cavities of a gneissoid granite pegmatite, associated with
emerald green beryl, monazite,
rutile, and other minerals. found in small striated and etched
crystals, much smaller than those of
Kunzite. Hiddenite is named after W. E. Hidden. North Carolina is the
only known locality for the chrome bearing green spodumene. A lighter green
colored variety that does not contain chromium is found in Brazil and some
other locations. Irradiated spodumene of any color turns a bright green
color which easily fades on exposure to light.
The
ordinary varieties of the mineral were once used as a source of lithium in
the manufacture of lithium salts, and the transparent varieties are used as
gems. Ordinary ash-grey spodumene is of no value as a gemstone; as noted it
was once used as a source of lithium salts, but easier sources exit and are
now worked.
For More information
on this gem see:
Hiddenite Spodumene
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