All- Since diamonds are formed in earth’s magma and pulsed to the
surface through quick explosive eruptions without changing
temperature or pressure does anyone know how a minute crystal of red
(ruby? garnet?) can become imbedded in the diamond? As far as I’ve
read, only diamonds and peridot come up from magma and if it’s a slow
ascent they will each become something else ,i.e. diamonds would
become carbon dioxide or recrystalize as graphite. Maybe there’s a
really simple explanation that goes by me. Help me solve this
puzzle, please Pat Kulla @ Patania’s
Since diamonds are formed in earth's magma
Scientists are unsure about the exact formation conditions for
diamonds: it is possible that they crystallise in liquid magma, but
it is also possible that they crystallise in solid rock.
and pulsed to the surface through quick explosive eruptions without changing temperature or pressure
The pressure and temperature change enormously. However, in a
kimberlitic explosive eruption, the diamonds are blasted to the
surface so rapidly that they cool down before they have time to
metamorphose into graphite.
does anyone know how a minute crystal of red (ruby? garnet?) can become imbedded in the diamond?
The red crystal you see is probably garnet. Ruby is also a
possibility, but ruby inclusions are MUCH rarer than garnet
inclusions (years ago, it was assumed that the red crystals were
rubies but this has been shown to be incorrect in most cases).
Basically, the diamond crystallises in eclogitic or peridotitic
rock deep below the surface of the Earth. As it grows, it can
enclose small crystals of the minerals around it. These can be
various different types of garnet (usually reddish, violetish or
purplish), or peridot (greenish crystals of olivine, forsterite,
etc.). The diamond crystal is then blasted up to the surface -
possibly four billion years later.
As far as I've read, only diamonds and peridot come up from magma
So do garnets, and several other minerals.
?
-Michael.
Registered Office:
Marks & Spencer p.l.c
Michael House, Baker Street,
London, W1U 8EP
Registered No. 214436 in England and Wales.
Telephone (020) 7935 4422
Facsimile (020) 7487 2670
Please note that electronic mail may be monitored.
This e-mail is confidential. If you received it by mistake, please let us know and then delete it from your system; you should not copy, disclose, or distribute its contents to anyone nor act in reliance on this e-mail, as this is prohibited and may be unlawful.
The registered office of Marks and Spencer Financial Services PLC, Marks and Spencer Unit Trust Management Limited, Marks and Spencer Life Assurance Limited and Marks and Spencer Savings and Investments Limited is Kings Meadow, Chester, CH99 9FB. These firms are authorised and regulated by the Financial Services Authority.
End of forwarded message
All- Since diamonds are formed in earth's magma and pulsed to the surface through quick explosive eruptions without changing temperature or pressure does anyone know how a minute crystal of red (ruby? garnet?) can become imbedded in the diamond? As far as I've read, only diamonds and peridot come up from magma and if it's a slow ascent they will each become something else ,i.e. diamonds would become carbon dioxide or recrystalize as graphite. Maybe there's a really simple explanation that goes by me. Help me solve this puzzle, please Pat Kulla @ Patania's
Hi Pat. Actually, diamonds don’t form in magma, they form in the
oldest, densest, most stable parts of the earth’s crust in areas of
the continental (not oceanic) plates called cratons, about 90 to 120
miles (140 t0 190 km) below the surface. They form along with other
minerals, including garnet, spinel, peridot and several others in
one of two types of rock; eclogite or peridotite. These two rocks
are necessary to lend carbon to the diamond formation process. The
diamonds (and the other minerals) in the eclogite stay in place in
the crust until a crack or fissure forms under the deposit. If the
right elements are available, some magma will form another mineral,
either kimberlite or lamproite. This new rock is no longer magma.
The kimberlite rises from below and carries the diamonds and other
minerals to the surface at an ever-increasing speed, until it erupts
through the surface at an estimated 186 MPH (300 kPH) for the last
1.5 miles of the trip. There are also plenty of fluids which expand
into gases involved in the process (kind of like when you open a
bottle of soda after shaking it up). Now, don’t get me wrong, the
kimberlite is still very hot, but the “expansion delivery” happens
too fast to revert the diamonds’ carbon to graphite (that does
happen, though…which is why, out of 6,000 known kimberlite pipes,
fewer than 1,000 contain any diamonds, and only about 50 had enough
worth mining and only about 20 are being mined today). So, the
expansion of gases and delivery speed are important for the delivery
to the surface. That also means that your assessment is correct;
that if its a slow ascent, the minerals become something else.
With all that being said, the answer is that diamonds form around
the other minerals in the eclogite or peridotite just as beryl can
form around phenakite, mica, pyrite, tremolite, etc. but in the
crust, not in magma. The kimberlite brings it up to the surface very
fast and, voila! we have a diamond mine in the making. In fact, when
the mining companies search and explore for kimberlite pipes, they
begin taking core samples which are examined for “indicator
minerals” such as garnet, spinel, peridot, and, of course, diamonds.
It’s a complex process, but the short of it is, if a lamproite or
kimberlite pipe is found to be “diamondiferous”, larger-scale
sampling is done until the pipe is determined to be worth mining.
This takes years. South Africa’s newest mine, Venetia, was
discovered in the mid-1970s, and went into production in 1991. Yep,
a long time, but it produces over 4 million carats of diamonds
annually. I realize this is a long-winded explanation, but please
forgive me…I just took my Graduate Gemologist final exam last
Wednesday 
James
I realize this is a long-winded explanation, but please forgive me...I just took my Graduate Gemologist final exam last Wednesday :-)
Showing off a bit then?
(like I should talk)
congratulations on a major achievement in your training.
The trick now is to remember all that stuff. I took my GG in 79. I
sure= as hell don’t remember all the stuff I knew backwards and
forwards back then…
cheers
Peter