Thanks to ASTROBLEME and Diamond Digger for the responses in my previous thread. I really do appreciate the time you've taken to answer some of my questions.

I still have many more questions, but I think I'll start with just a couple and some observations.

Is this what I'd be looking for as far as kimberlitic type material?

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Most of it is very black until after it's been exposed to the weather, at that point a yellowish and in some areas a rusty red sort of film starts to form on the outer surface. It's very crumbly, I can break up a lot of it with just my hands, or a light tap or two with a hammer. Most of it is fine-grained, but there are chunks that look more like concrete, and then there are some with more of a crystalline appearance. It's fairly heavy and has a lot of iron in it. After breaking it up about 1/3 to 1/2 can be picked up with a magnet. I also have a lot of nasty yellow clay mixed in with the sand/gravel, which is quite different from the reddish brown clay that I'm used to seeing in this area. If you wash the sand/gravel with water you get a nasty yellowish muck that takes quite a while to settle. Is that what you guys refer to as yellow ground?

Hello TheRookie,

First a little background to help everyone understand more about diamond deposits. Prospectors, from the first diamond discoveries near Kimberly Africa, refer to any igneous rock containing diamond as kimberlite. This practice survives to this day although many geologists break out the types in detail and apply the proper nomenclature to the rock. Ideally, for kimberlite that has $ values, you'd want to have rock from the very deep diamond-stability zone that has erupted through the crust very quickly in order to keep most of the diamond crystals preserved. I think this eruptive process is triggered by large meteorite impacts so searching near those impact sites is what I would recommend.

The problem that modern diamond prospectors have is kimberlite rocks are complex hybrids consisting of crystals originating from 3 very deep mantle sources. The overall minerology of any given kimberlite type rock from each of the 3 mantle sources varies widely and accounts for the thousands of different compositions observed world-wide. This means that kimberlite looks different between locations and many times even within the same pipe emplacement. I have collected a wide variety of kimberlite specimens to help me better understand what to look for. You could also use kimberlite photos found on the www but an in-hand speciment is best. Garnets are a key component found in kimberlite but not all garnets are indicators of kimberlite. The minerals common to kimberlite include garnet lherzolite, garnet harzburgite, chromite harzburgite, spinel lherzolite, websterite, eclogite, grosspydite. You may also find peridotites containing phlogopite, potasium richterite, yimengite and hawthorneite. This mineral identification is far beyond what most diamond prospectors are accustomed to. I've spent lots of time and money running analysis and employing diamond savvy geologists to make sure I am finding what I need to when I'm out in the field. Most folks don't have the persitence in order to do that work but if you can seek to understand and look for what is referred to as the MARID suite of minerals, you will have a good handle on the more easily identified components of a kimberlite rock. MARID stands for mica, amphilbole, rutile, ilmenite and diopside. If your yellow ground or blue ground samples show these MARIDs... along with the proper garnet chemistry... then you likely have a kimberlite rock. MARIDs are best observed under high magnification and ideally by examination of a thin section prepared from the rock sample. Unfortunately, from the photo, I cannot see any MARIDs. If you are in a location where diamondifeous kimberlite has eroded, you should be able to find diamond(s) by using basic panning techniques. After all, the best indicator for diamond is diamonds.

Keep in mind that there are about 5,500 kimberlite pipes world-wide. Out of those known pipes, about 500 contain diamond. Only 50 or so pipes have enough diamond to profitably mine. If you can locate what is called a pan that develops over an eroded pipe, you can recover substantial quantities of diamonds that have been concentrated by Mother Nature. I would encourage you to have a competent geologist examine a specimen or two of your rock finds to formulate a proper answer to the "is it kimberlite" question.

Best Wishes,

ASTROBLEME

I understand what you mean when you say that a hand specimen is superior to looking at pictures. I've checked some of the rock shops in the area, but so far haven't had any luck finding kimberlite specimens. I think I'm going to take advantage of Metropolitan State U's free mineral identification offer as I've tried contacting the geology departments at some of the universities closer to me, but none have even bothered to reply. Before I do though, would you be interested in having any? I could post some close up pics of some of the ones I'm planning to send to Denver and if there's anything you think you'd like I could send it your way. If it's not something you need, or something you've already got, you could do whatever you like with it. If it's from the lamprophyre near here maybe it'd be different enough in composition that you might find it useful. As to that lamprophyre, it is reportedly diamondiferous, though they do say that it doesn't contain economic concentrations of diamonds. I have to wonder just what that means, though. Wisconsin is a really difficult area to operate any type of mining operation. All one needs to do is to look up the history of the Flambeau mine in Wisconsin and the litigation involved. The lawyers probably made more than the miners. From what I can tell from looking at glacial maps the Six Pack Lamprophyre would have been directly up-stream (up-ice?) of my location. I don't know, even if this does turn out to be lamprophyre or kimberlite I've found, if it even came from that location. I've read that they generally form in clusters. Right? For all I know, it could be from an undiscovered, and not diamondiferous pipe. Anyway, here's one particular specimen I found interesting.




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TheRookie..

Here are a few pictures of Kimberlite they are on the site and on the net what you are looking for is Purple Garnets, ilmenite, feldspa, unikite etc
Have fun.
Pic1: Note the green Chromium diopside

Pic 2: Lava ash mix with Kimberlite

Pic 3: The usual indicators close to a pipe

When hunting for a pipe look for these indicators ten hand wash for the green Chromium Diopside crystals and then you know you are within .25 miles from the pipe Cr diopside is brittle and does not travel far, follow it till you it the blue/black rock

Pic 4 here you can see the weathered Kimberlite and the green lava ash, green indicate Chromium Diopside no chromium no diamonds..
Have fun out there.
DD

See above

I didn't realize that unakite was an indicator I should be on the lookout for. I have a boulder, well, it was a boulder, much of it is badly decomposed, that was partially altered to what appears to be unakite. Kinda cool the way the altered stone is far less decomposed than the rest of it. I'm working in an old stream bed, I was actually hand digging a well for outdoor use when I came across all this stuff. There is an old stream bed buried in my yard, under about 4 feet of red clay. The boulder that looks like it's partially unakite was near the top of the sand/gravel & was too big to move, so I dug down next to it. A couple days later a rainstorm washed the sand/gravel out from under it & it started to fall down into the hole. I pulled out about 5 chunks of it, the largest about 80-100lbs. but a lot of it just disintegrated. I cut a small slice out of a piece of it with a hand grinder, & exposed a vein of the green in a small pc.

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In this pic you can see the transition from altered to unaltered stone.

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Here's a small green stone I found the other day. Not sure if it's diopside or what.

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Today I found this. What may come out looking black is really a very, very dark green.

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Hi,

Not there yet, on the pictures it is not easy to id rocks but that looks like granite and maybe copper.
Chromium diopside is a brittle see though crystal.
Keep searching!
That's how money is made!
DD

Like on this picture from the Master Mr Dan Hausel

Some Unakite for reference in the field.
DD

I have compared what I have to actual hand samples of unakite. The color is a bit washed out in the pics and they're unpolished but a side by side, in hand comparison looks good.

Just a quick reply to let you guys know where I'm at here. I'm currently working through a pile of sand/gravel/yellow clay mix from this old stream bed. I'm classifying to -1/8" to wash out the sand & clay and putting the larger gravels aside. I've got a very limited water supply available, less than 50gal./day, and the clay takes forever to settle out, so I can only wash about 1/3 yard or so per day. I had hoped it would go faster, but it is what it is. Hopefully later this week I'll be able to clean out my settling ponds and run some gravels through my drop riffle sluice. Then I'll know if I have just gravel for my driveway or something more. Will update soon.

Got a new toy the other day. A digital USB microscope. Thought I'd share a few pics. These are what my "black" sands look like up close and personal.

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More pics. These are black sands that I separated out with a cheap harbor freight pickup magnet.


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Cool, thanks for posting these.

Thanks, I'm pretty happy with the microscope, so far. Picture quality is pretty darn good for a 35 dollar toy.