Jeff Lawrence on fri 13 jul 01
Hello,
I am curous about some sand from a black sand Kaui beach.
There is a high proportion of sand-sized particles of
green/yellow glass (transparent, conchoidal breakage)
Larger chunks show clearly that green/yellow glassy chunks
appear as little nuggets in new black basalt (flows from
the last thirty years).
Anybody have any info about the chemistry involved?
TIA,
Jeff
Jeff Lawrence jml@cybermesa.com
Bruce Girrell on fri 13 jul 01
> I am curious about some sand from a black sand Kaui beach...
> Anybody have any info about the chemistry involved?
Jeff,
The green stuff is olivine, also known as chrysolite. It is magnesium iron
silicate - (Mg, Fe)2SiO4.
Basalt is composed primarily of plagioclase, pyroxene, olivine, and
magnetite, but there is a host of other lower percentage minerals as well.
Plagioclase is feldspar in the Ca/Na group, as opposed to orthoclase, which
is potassium feldspar.
Pyroxene is (Mg,Fe,Ca)2Si2O6. The general pyroxene formula is XYZ2O6, where
X = Mg+2, Fe+2, Mn+2, Li+, Ca+2, Na+, Y = Al+3, Fe+3, Cr+3, Cr+3, Ti+4,
Mg+2, Fe+2, Mn+2 Z = Si, Al+3, Fe+3 The most common form is
(Ca,Mg,Fe)2Si2O6.
I'll leave the issues about the legality of collecting the sand up to you.
Bruce "I've _never_ done anything illegal (cough, cough)" Girrell
Wade Blocker on fri 13 jul 01
Jeff,
I received a small quantity of black beach sand from Hawaii. I wedged it
into some porcelain clay. The result was a body spotted with brown spots,
similar to ,but more attractive than wedging either iron particles or
manganese into the clay. Obviously iron bearing sand from volcanic
eruptions. Mia in ABQ
Michael Banks on sat 14 jul 01
The green/yellow stuff sounds like olivine, Jeff. This mineral is common in
Hawaiian basalts. It is iron magnesium silicate ([FeMg]2SiO4).
The iron-rich version is called fayalite (deep green) and melts at 1205oC,
the magnesium end-member is called forsterite (colourless) and melts at
1890oC. The basaltic olivines are generally somewhere in-between fayalite
and forsterite in composition and are yellow to yellow green in colour. .
Such continua are called solid solution series. Large flawless olivine
crystals are the gem peridot.
In ceramics, forsterite refractories are made by sintering magnesite, talc
and kaolin. Fayalite forms naturally in over-fired iron-rich clays. The low
melting point of fayalite is the general cause of brittleness and
vitrification of red clays when overfired.
Cheers,
Michael Banks,
Nelson, NZ
(back to lurking after a gallivant around New Mexico & Ariz)
----- Original Message -----
Jeff Lawrence wrote:
> I am curous about some sand from a black sand Kaui beach.
> There is a high proportion of sand-sized particles of
> green/yellow glass (transparent, conchoidal breakage)
>
> Larger chunks show clearly that green/yellow glassy chunks
> appear as little nuggets in new black basalt (flows from
> the last thirty years).
>
> Anybody have any info about the chemistry involved?
Arnold Howard on tue 17 jul 01
I lived for two years on the Big Island near Kapoho. The black and
green sand beaches there are beautiful.
The Big Islanders believe that if you remove the sand from the
island, the goddess Pele will seek retribution. This believe is so
firmly ingrained that even visitors from the Mainland accept it.
One of the most interesting displays I saw in Hawaii was at the
Kilauea National Park. Under a glass display case were odd bits of
lava with letters explaining that the visitors had returned the
lava due to a string of bad luck. One person even returned a pair
of tennis shoes with sand embedded into the soles.
I just wanted to add folklore to the other excellent posts that
covered the chemistry of the sand.
With best wishes,
Arnold Howard
Paragon
--- Jeff Lawrence wrote:
> Hello,
>
> I am curous about some sand from a black sand Kaui beach.
> There is a high proportion of sand-sized particles of
> green/yellow glass (transparent, conchoidal breakage)
>
> Larger chunks show clearly that green/yellow glassy chunks
> appear as little nuggets in new black basalt (flows from
> the last thirty years).
>
> Anybody have any info about the chemistry involved?
>
> TIA,
> Jeff
>
> Jeff Lawrence jml@cybermesa.com
>
>
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