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“Sand to Chips” - what’s the real story?

One of the thorny issues that I grappled with in writing the book was how to
review the staggering number of ways in which sand is important in our lives -
in the end, the diversity was so overwhelming that I resorted (as readers of the
book will know) to an alphabetic medley approach; interestingly, it would seem
to be a chapter that is often highlighted in reviews and comments as
either highly entertaining or awkward. In my ruminations about how to weave all
these disparate topics in to  a narrative, one idea had occurred to me: given
that an immediate and recurring (if subconscious) encounter we all have
with quartz sand is every occasion that we use an electronic device, why not
tell the story, the journey, of a sand grain from its geological origins to the
silicon chip in the computer on which I was writing?

“Sand to chips - a biography” - seemingly a simple task, this proved anything
but. To begin with, given the need for various but rigorous levels of extreme
purity in silicon-based manufacturing, just any old sand won’t do - the raw
material has to be as pure as possible to begin with. As I wrote:

First of all, the public is understandably more interested in the technology
of making the silicon chip than in its provenance in a sandbank by a river
somewhere. Second, the absolute volume of semiconductor-grade silicon is only a
small fraction of all silicon production. But more important, a small number of
companies around the world dominate the technology and the market, and while
their literature and websites go into considerable and helpful detail on their
products, the location and nature of the raw materials seem to be of “strategic
value,” and thus an industrial secret. I sought the help of the U.S. Geological
Survey, which produces comprehensive annual reports on silica and silicon (as
well as all other industrial minerals), noting that statistics pertaining to
semiconductor-grade silicon metal were often excluded or “withheld to avoid
disclosing company proprietary data.” The survey staff were, as always,
extremely helpful, but were themselves perplexed that such an apparently simple
question was not simple to answer. They put me on the trail of a number of
sources, but telephone and e-mail inquiries did not shed a great deal of light.
What I could deduce is this: the common source of silica for manufacturing the
high-purity grades of silicon used for, among other things, silicon chips is not
loose, unconsolidated sand from a beach or river sandbank, but sand that has
already been ultrapurified by nature: quartzite.
Quartzite is a rock that was originally a silica sandstone; it has been so
deeply buried in the Earth’s crust, cooked by such high temperatures and
pressures, that many of the impurities have been distilled out and the sand
grains completely annealed and welded together. Hit quartzite with a hammer and
it rings like a bell because of its hardness, purity, and uniformity. Hit it
hard enough and it breaks across the ghosts of the grains, not around
them. Quartzite can be well over 99 percent pure silica. Grind it up to a powder
of a consistent grain size and it’s a good starting point for making
silicon.

The geological kitchens of the Appalachians were good at making quartzites,
and my research (including phone calls to sand and gravel suppliers) led me to
one possible source:

The Coosa River, for example, originates close to the border of Georgia and
Tennessee and, together with its tributaries, drains a large and geologically
diverse area of Appalachian rocks, including quartzites. It crosses from Georgia
into Alabama, where it joins the Tallapoosa to become the Alabama River. As it
does so, it enters the broad coastal plain, slows down, and dumps its sediment
load. Large volumes of aggregatesfor all kinds of industrial purposes
are extracted in this part of the country from the sediments of the Coosa and
other rivers, but among those everyday aggregates are pebbles of great
value—pure quartzites from the kitchens of the Appalachians. And those, I
believe, are one source of raw material for high-grade silicon. So it’s true
that computer chips are made from sand—but sand that was first deposited several
hundred million years ago.

But the confidence level that I (and the USGS) had in this being a definitive
example led me to abandon the sand grain biography idea. Then, earlier this
week, the whole issue arose again: BBC Radio in the UK had a programme (it is
the BBC, hence the extra “me”) called “Chips with Everything” and
an associated article titled “Silicon Valley’s
Secret Recipe.” The thirty-minute broadcast is well worth listening to, for
the “Silicon Valley” referred to is in the Blue Ridge Mountains of North
Carolina, around the small community of Spruce Pine which calls itself the
Mineral City - for good reason. The programme is culturally fascinating but also
highly informative with respect to silicon chip technology - and I learnt
something that I had missed in the opacity of my earlier research.

The reason the Spruce Pine calls itself the Mineral City is that in the
surrounding hills is a treasure trove of precious and highly valuable industrial
minerals - including some of the purest quartz in the world. These minerals,
exploited since long before the ancestors of today’s residents arrived, are
contained in igneous rocks, solidified from molten material deep below the
earth’s surface; but these are special, rocks that are made up of unusually
large and unusually pure, crystals - rocks called pegmatites. Below is a
photograph of one of these (thanks to Callan at NOVA
Geoblog), with large feldspar crystals embedded in quartz. It was long
thought that these unusually obese crystals formed because the cooling rate of
the molten rock was extremely slow, but this apparently logical model has been
replaced by recent research that suggests that the cooling rate was unusually
rapid, faster than the rate of crystallisation could keep up with.

The hills around Spruce Pine have been described as the most valuable
strategic acreage on the planet. Sixty-eight-year-old Ira Thomas, a
ninth-generation Spruce Pine miner who used to dig up aquamarines and prospect
for mica as a child justifies this description: “Because the world runs on
computers, we all know that now. And if we locked the gates to Mitchell County
they could not make any more computers.” As a consequence, the quartz pegmatite
mines are protected by security akin to the Pentagon or the Bank of England.
Spruce Pine is billed as the world’s only source of this uniquely pure quartz -
this is geologically probably not quite true, but it is by far the world’s major
supplier of a raw material that sells for $50,000 a ton.

But so what was my revelation? Simply that the Spruce Pine quartz is valuable
notas the source of silicon for chips, but as the material for making
the crucibles and other bits of kit needed to process electronic-grade
silicon. Silicon can be extracted from any quartz relatively easily (you can do
it, albeit somewhat dangerously since silicon is an excitable element, in your
kitchen from beach sand); but to process it to the level of purity needed, then
ultra-pure equipment is essential - and it’s made from Spruce Pine quartz. The
level of silicon purity for a chip is extraordinary: electronics-grade silicon
has to be at least 99.99999 percent pure - referred to in the trade as the
“seven nines” - and often it’s more nines than that. In general, we are talking
of one lonely atom of something that is not silicon among billions of silicon
companions. Or, as a Dow Corning scientist, put it:

Imagine stringing tennis balls from the Earth to the moon, and wanting them
all to be yellow. He said this would take about 5.91 billion tennis balls. For
the color coding to be of semiconductor quality, “you could only tolerate two,
maybe three that were orange,” Lane said. For solar cells, which are slightly
less demanding, Lane said, “You could tolerate five or six orange balls.”

Following up on the BBC material, I came across a useful series of articles
on Geek.com, which, in turn, led me to a press
kit put out by Intel, titled “From Sand to Silicon: the Making of a
Chip.” And there, to my delight, at the head of the document is an image of a
pile of sand. One of the Intel images is at the head of this post, and in the document is accompanied
by the description:

Sand
With about 25% (mass) Silicon is –after Oxygen –the second most frequent
chemical element in the earth’s crust. Sand –especially Quartz -has high
percentages of Silicon in the form of Silicon dioxide (SiO2) and is the base
ingredient for semiconductor manufacturing.[my
highlighting]

The silicon is purified in a series of technologically sophisticated (and
highly secret) steps; to the right of the pile of sand is melted silicon, and
then a “Mono-crystal Silicon Ingot … produced from Electronic Grade Silicon.
One ingot weights about 100 kilograms (=220 pounds) and has a Silicon purity of
99.9999%.” (Why six, not seven, nines?)

So there we have it - sand, or potentially sand in its quartzite incarnation,
isthe source of raw silicon for electronic chips. But I am no further
forward on identifying geologically which sands - or sandstones, or quartzites -
are the sources. The quest continues - if anyone can shed light on this, I would
be hugely grateful: I can provide an update for the paperback edition of Sand!

[My profound thanks to Pete Modreski at the USGS for his continuing help throughout this
quest. And there are other sources of high purity quartz in the world, among
them from Norway: the NGU, the Norwegian Geological Survey, has an excellent web
page, in English, on high purity quartz -  http://www.ngu.no/no/hm/Georessurser/industrimineraler/Kvarts-og-kvartsitt/Hoy-ren-kvarts/]

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Comments

Jules (2009-08-07):

Fascinating,thanks for the continuing research Michael.
I knew that IC grade silcon had to be extremely pure,but the connection to Spruce Pine was new to me also and is a place situated in a very beautiful area of my adopted state that I will have to visit again.

Sandglass (2009-08-08):

Unfortunately, and inevitably, a visit to google earth will show that substantial areas of Mitchell County have lost some of that beauty.

Jules (2009-08-08):

Yes(sigh…)I know and the the Blue Ridge Parkway and its supporters are trying to save as much of the area in their viewscape as possible. The development going on there and along the rest of the VA/NC Blue Ridge is nothing though compared to the major ecological and social destruction going on in the mountain top removal areas of West Virginia and the Appalachians.
It is becoming increasingly controversial and affecting more people as well as the environment,so I am hoping that the protests will result in some abatement of this unsustainable mining technique. We have to mine for natural resources but there are political and corporate entities heavily involved who refuse to see that as with other excessive extraction processes of the past, this process cannot be sustained without irrevocable damage to the places that these industries and their workers live in and depend on.

Sandglass (2009-08-08):

Yes - it’s unbelievable that this devastating mining technique, an offense to the landscape and to rational policy, continues. There was an article about it in the British press just last week -
http://www.guardian.co.uk/environment/2009/aug/04/mountaintop-mining

Patrick Darling (2009-08-24):

Wonderful article Michael. I’m very glad the timing of our post on the intel.com Press Room was useful for you in your work.
Patrick Darling
Online Media Relations Manager
http://www.intel.com/pressroom