My Take on Achondrites

[John B.]

Hi All

At the Mike Blood Auction during the Gem show this year there were several speakers. One gentleman did a real informative speach most of which I even understood. His particular interest is in the study of achondrites ( very low metal rare types of space rocks. As the planets acretiated ( formed ) between Mars and Jupiter. As there size and masses grew so did thier gravity as their gravity increased so does the heat and pressures within. As in the center of our planet the cores of those were molten Iron Nickle that came from somewhere the mantle of that core formed the stoney irons ( Mesosiderites and Pallasites) above that mantle is a layer of rock that was leached by heat and pressures of most of it's iron nickle ( the Achondrites) . The varying types are from different levels of depth or different planetary sources. The very surfaces of those planets and smaller asteroids that hadn't grown enough in size to build the gravity that creates the heat to alter the chondrules that were formed earlier and make up ordinary chondrites. The gradeing of 3 to 7 in ordinary chondrites is the presence and preservation of chondules. A 3 grading means alot of unaltered chondules and a 7 grade means no chondrules present and they were altered by heat , pressure or shock. Chondrules are the small balls of silicates that are thought to have coalessed from vapors after the big bang. The asteroid belt between mars and jupiter is thought to have been made by at least 2 planet sized bodies that collided in our solar systems early make up and is now the asteroid belt !! The carbonacious chondrites are associated with comets !! There may also be an assosiation with urilites which are carbon rich hence the diamonds ?? I Think ?? Any input to this or corrections is truley welcomed but this is my take on it ?? Happy Huntin John B.

[Goldfinger]

Hi John B:

You're certainly no babbling idiot. :???: You're our meteorite expert. :wubu: and I've learned quite a bit from you.

The explanation gave me some insight to these rare finds. I know diamonds only form under certain conditions- at least here on Earth and am still a little perplexed about these small diamonds being found in meteorites.

Steve

[gatorguy]

Diamonds are pure carbon and are formed under high heat and tremendous pressure. Don

[John B.]

HI Steve

I'ld say your pretty well screwed if your relying on my teachings :hahaha: !! There are some real wizzards on meteorite identification and origins ! I only have pretty basic field knowledge from my own experiences and what I've seen at the shows and just some basics but I have the passion for the hunt !! If you really want detailed and in depth info the meteorite list at meteorite central has some real smart folks and scientific minds among it's ranks . I try not to post on there cause I don't want too sound toooo stupid :???: !! Happy Huntin John B.

[Paleface]

John B.,

I have to agree with the current posts and past posts that relate to your knowledge of meteorites. I have learned a whole bunch from you and I think it is because you have a way of taking the really complex information and putting it into terms that most of us can understand. Book learning only goes so far, you have the hands on experience, in field experience, as well as many years of the Tucson show under your belt. Been there, done that--- is always a better teacher than a book. When people that have been there and done that, speak, I take notes... I Read about 15% of the posts on the Met List, and do agree that there are some real meteorite wizzards on there. I have never posted on the List, mainly because of the fear factor. I have a real distaste for wizzard fights..... :hahaha: I just lurk :ninja: and learn....

Keep up the great informative posts. I like em

Jim

[Nugget Shooter]

Yup JB,

If it wern't for you I and many others may still be kicking them aside :bang: The time you have taken to educate others in meteorite collecting and ID has in my opinion been of great benifit to science as folks you have enlightened find new specimens and bring them to light! I know of one for sure called Trilby Wash ;)

Thanks John!

Bill

[Hveragerthi]

Diamonds are pure carbon and are formed under high heat and tremendous pressure. Don

I have been reading through old posts and came across this one. I wanted to clarify a few things.

Diamonds are formed from graphite. Basically carbon forms in to graphite, then in to a diamond under the right circumstances. Basically high temperature in the absence of oxygen. It is generally thought that high pressure is also required, but this is not quite true. Synthetic diamonds have been manufactured for about 16 years or so under very low pressures (1/10) of an atmosphere. Originally they were formed from running methane gas past a heated tungsten coil, which knocked the carbon out forming a diamond film. I tried a similar experiment about 15 years ago in an attempt to make larger diamonds. But I improvised a little too much and the pressure built up and....... Let's just say my roommate was a little pissed off when she found my experiment all over the walls and ceiling :innocent0009:. A company called Apollo has taken it further and is now doing a similar process, substituting a microwave beam for the tungsten coil, which has allowed them to make larger diamonds through layering.

Other companies, such as GE and Gemesis have been using high temperature/high pressure processes to form diamonds. GE has been doing this since the 1950s, and dopes their diamonds with boron, making a blue, semi-conductive diamond. Although, up until a few years ago they were unable to grow diamonds beyond 1 carat before they started to decompose. They reversed the ratio of carbon 13 and carbon 14, if I recall right, which stabilized the diamonds, and they are now able to grow diamonds beyond 1 carat. It has also been found that chromium makes an excellent catalyst for the synthesis of diamonds. And synthetic diamonds manufactured from buckeyballs actually create diamonds harder than natural diamonds.

The hardness of diamonds comes from their structure. In basic carbon the arrangement of atoms is somewhat spaces and very random, which makes the carbon soft and light. When converted to graphite, the atoms arrange in rows forming planes that slide against each other. Thus the slickness of graphite. When converted to a diamond, the atoms go back in to a random order, but are more tightly compacted creating a greater strength and density. In fact, the density is so great that light passing through a diamond is slowed down by half its normal speed.

Diamonds range in color quite a bit. Shades of purple (the rarest), to red, orange, yellow, green, black, blue, and brown. They get their color from several things. Impurities are of course one way. For example, boron will form blue diamonds. Red, yellow, and green diamonds can form from nitrogen, depending on the concentration. The second way colors “form” in diamonds is actually a optical effect, as opposed to an impurity. Vacancies in the atomic structure can affect the way light goes though the diamond, and thus the color it appears to us. For instance, let’s say that a pure white diamond has a structure of C-C-C-C-C. If you expose this diamond to radiation, the radiation can eliminate some of the atoms in the structure: C-C- -C- -C-C. These vacancies in the atomic structure again change the way we perceive the color of the diamond.

Diamonds are actually extremely plentiful in the earth’s crust. The problem is getting them up to a shallow enough depth for us to collect while still intact. Diamonds are very unstable when exposed to heat and oxygen. Exposing a diamond to a few thousand degrees in the presence of air will cause the diamond to revert back to graphite. This is important since it could go a long way to explaining how diamonds form in meteorites as well. Diamonds are found in volcanic vents known as kimberlites and lamprorites. The diamonds are not formed in these pipes, but rather brought to the surface, or closer to the surface within these pipes. The reason we do not find diamonds in some volcanic pipes all boils down to temperature. Volcanic pipes originating from way deep in the earth produce extremely high temperatures. As this extremely hot magma comes up through the layer of the earth rich in diamonds, the high temperature, and the presence of oxygen at the surface literally vaporizes the diamonds in to the carbon dioxide gas often seen in volcanoes. Kimberlites and lamprorites are much shallower pipes, and do not contain as hot of magma as found in the deep pipes. As this cooler magma and steam are forced upward, the diamonds in their path are carried up in the magma intact to the surface, or at least a lot closer to the surface.

In meteorites I would assume then that the diamonds are formed from the compression temperature, or other high temperature, on the carbon within the rock in the absence of oxygen. In this manner the carbon would convert first to graphite. Then, because of the lack of oxygen, would convert to diamond, instead of carbon dioxide. The presence of certain metals, such as chromium, found in some meteorites could be catalyzing the process.

[pallasite alex]

"When converted to a diamond, the atoms go back in to a random order"

crystals all have specific structures so i doubt diamond is any different(cubic system). Also unfortunately they are micro diamonds made by solar wind and meteorite impacts.

chondrules are not from the big bang but formed from left over material from supernova. big bang made only light elements, while chondrules have iron and nickel, as well as heavy elements like uranium. type 2 supernova i think. they are around 4.5bill yrs old and big bang was 13.4billion yrs ago i think, my memory isn't that good after a few G yrs.

have any of you guys read about the recent supernova in that distant galaxy, pretty darn amazing eh?

regards

pallasite alex

[Hveragerthi]

"When converted to a diamond, the atoms go back in to a random order"

crystals all have specific structures so i doubt diamond is any different(cubic system). Also unfortunately they are micro diamonds made by solar wind and meteorite impacts.

regards

pallasite alex

I guess I used a poor choice of wording. The atomic arrangement is more random than with graphite, which is what I was trying to point out. By the way, not all diamonds form a cubic structure, and diamond films are amorphous, so they don't have a crystalline structure at all. In addition, the vacancies in the atomic arrangement will further randomize the structure. Also, twisting of the overall structure may also occur, which accounts for the colors of some diamonds. So diamonds do not always have a specific atomic arrangement.

I am not sure what you meant by "unfortunately", but I did discuss the formation of diamonds by meteorite impacts:

"In meteorites I would assume then that the diamonds are formed from the compression temperature, or other high temperature, on the carbon within the rock in the absence of oxygen. In this manner the carbon would convert first to graphite. Then, because of the lack of oxygen, would convert to diamond, instead of carbon dioxide."

I have never heard of solar winds forming diamonds though. Do you have any information on this process?

[Jayray]

WOW, JB stirring the pot in the intellectual soup kitchen... Very insightful information on the structure of diamonds and such. Keep up the great posts!!! Jason :;):