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14th Jan 2020 02:31 UTCFrank K. Mazdab Manager

does not look like a lamproite to me, but if you have money to burn (and in this case I do think burn), have a thin section made.  A polished thin section will set you back somewhere between $35 and $50, depending on the facility that prepares it. No better way to examine a rock, especially a medium to relatively fine-grained rock, than to look at a thin section of it under a petrographic microscope. Some combination of olivine, pyroxene, potassic amphibole, phlogopite and/or leucite should be recognizable in a lamproite, depending on its variety. And of course diamonds, if they're not plucked out due to their hardness, would appear very high relief in plane polarized light and isotropic under crossed polarizers.

Some labs that make thin sections will examine them for you at your request (for a per hour or occasionally per sample rate, and not usually cheap), or you might be able to pay a grad student at a local university with petrographic experience (rare these days) to do it for you for less. If it's an especially compelling sample, a polished thin section can also be microprobed (that costs money too).  But hey, if it's a lamproite loaded with diamonds, who's counting the coinage, am I right?  LOL

14th Jan 2020 02:51 UTCDan Chang

Crystals were tested by silicon carbide sandpaper for hardness and hydrophobic property also tested as shown. At this stage, I just want to do some preliminary/quick test on the rocks to make sure it's ultrabasic/ultrapotassic. If the selected crystal bearing rocks passed preliminary tests, they will be further tested by Raman spectroscopy/CRIS, XRD, XRF, and ICP-MS, or maybe SEM....  Polished thin section would be a great choice then. Thanks.

14th Jan 2020 02:43 UTCPaul Brandes Manager

Agree. That is not a lamproite.
From what I can see, looks like a piece of massive quartz or quartzite.

14th Jan 2020 02:54 UTCDan Chang

Quartz or quartzite can't survive SiC sanding even if DS2 is that way off. Isn't it?

14th Jan 2020 04:48 UTCDoug Daniels

Note that grinding the sample to a powder then dissolving it would do - nothing.  Most all rocks are rather insoluble in water (as opposed to, say, table salt).  Even if you could dissolve it in water and measure the pH (acidity), it wouldn't tell you if the rock is "ultrabasic", any more then doing the same with a granite would tell you it is "acidic".  The rock terms acidic, intermediate, basic, and ultrabasic refer to  the overall silica content of the rock.  They are older terms whereby silicates were considered salts of a "silicic acid", so a rock with lots of silica was considered "acidic", whereas those poor in silica were considered "basic" or "ultrabasic".

14th Jan 2020 06:46 UTCDan Chang

Diamond indicator Pandanus candelabrum grows in the soil on top of diamond-rich kimberlites/lamproites which crops out and weathered into soil mixture. Experts suspect that the plant has adapted to kimberlite soils which are rich in magnesium, potassium, and phosphorus. P. candelabrum's surrounding soils are mostly measured at around PH 7~8 or even higher. I think crushing a lamproite into powder to make solution just mimics weathering.

I agree an overall content analysis would be desired. But, lamproite compositions are widely varying except SiO2 must be <45% as an ultrabasic property, thus I don't know what exactly to look for beyond that. For now, I need to find something quick and preliminary so I don't mistake a felsic rock for an ultrabasic one easily.

How likely the PH range of ultrabasic lamproite-powder-solution goes below 7 barring any inadvertent mistake? Or, the other way around, how likely a felsic rock powder solution goes above 7?

14th Jan 2020 07:53 UTCFrank K. Mazdab Manager

weathering of rocks, whether lamproite or granite or whatever, typically takes place on geologic time scales, so powdering your rock and adding it to a beaker of water will not tell you if you have an ultramafic (=ultrabasic) or felsic (=acid) rock... in fact, I doubt you'll learn much more than how to make muddy water. Your wild pandanus are growing on rocks that have been weathering for millions of years, not just for days.

If you really want to know your rock's chemistry, there's no skimping... you'll need to get a whole rock analysis (probably ~$30... perhaps google "whole rock analysis commercial labs") and have a thin section made.  Why do both, you might ask?  Because not all low-silica rocks necessarily have to be igneous rocks (consider a calc-silicate rock or even a marble... in the latter case, silica can be as low as essentially 0 wt%, but clearly it's not an "ultramafic" rock [although ironically, a carbonatite of the same composition would be, so go figure]). So you would likely need to evaluate the rock's chemistry (whole rock analysis) and the mineralogy (petrography).

However, if you can evaluate the mineralogy from the hand sample alone, that's great and will save you some money and effort. But lamproites are often quite fine-grained, so trying to figure out the minerals with just a hand lens may not be good enough.

By the way, I'm still very skeptical your rock is a lamproite... I've seen a few lamproite/kimberlite examples.  I host a website specifically featuring "exotic" igneous and metamorphic rocks:
and your rock doesn't resemble any of the more unusual mafic/ultramafic igneous rocks I've looked at before. Still, if you are genuinely serious about ID'ing your rock, you're going to have to have it done by professional means (no "internet"-theory beakers of water methods), and also be willing to pay for the effort.

14th Jan 2020 08:34 UTCDan Chang

Crushing a lamproite into powder to make a solution may not be a 100% mimic to weathering. Some low-silica rocks may not be igneous. Points duly noted. But, in general, doesn't ultrabasic powder solution tend to be more basic and felsic more acidic? Do you expect to see something else more likely? I'm considering testing my hand samples, but try to run it by you guys first. If it really makes no sense whatsoever, why bother testing it? As long as it's not a far-fetched idea, even though not 100% perfect, I will give it a try. 

14th Jan 2020 09:37 UTCFrank K. Mazdab Manager

Dan Chang  ✉️

But, in general, doesn't ultrabasic powder solution tend to be more basic and felsic more acidic?
Well, I suppose in theory yes.  As Doug noted above, the term "acid" for silica-rich igneous rock derives from the fact that SiO2 is the "acid anhydride" of silicic acid, and it's the dominant "acid" oxide in rocks (others would be P2O5, SO3, and the like); similarly, "basic" rocks are rich in oxides that would nominally form bases in water, with particularly MgO (the "basic" anhydride of Mg hydroxide) considered.

But the problem with your idea is that the oxides that are sufficiently water-soluble to potentially affect your solution's pH (like CaO or MgO) are not present as such in rocks, but are tied up in minerals like olivine and pyroxene (the main exception being quartz, a "free" oxide present in many rocks). But those minerals and also any quartz are all notoriously insoluble in water... I'm talking part per million solubilities!

So it's unlikely the trivial amounts of dissolved minerals you'll be able to put into solution will have any noticeable effect on the water's pH. In fact, atmospheric CO2 or possibly NOx or SOx if you live in a polluted urban area (these gases are other "acid anhydrides") will probably have a greater effect on your sample's pH than the rock powder.

Anyway, I've spent way more time in this thread than I should have. My opinion is that it's a far-fetched idea. But if you want to spend an afternoon crushing up rocks and making mud, who am I to say you're wasting your time?  By all means, knock yourself out!

But be aware that there's a well-known axiom that a little bit of knowledge can be a dangerous thing.  I suppose spending fifty or sixty bucks on some analytical work might not be a bad investment if you learn a little petrology from the experience. But maybe don't be so quick to invest your life savings into your new "diamond" mine if your beaker of mud reads >7.0... just sayin'.

14th Jan 2020 11:09 UTCDan Chang

Frank, I really appreciate your time and efforts. As long as it is not too far from a theoretical point of view, I would be willing to test it.

From a practical viewpoint, you brought up some possible ramifications driven by the minerals in the rocks which can turn the table. I will take it with a grain of salt on picking the right sample for the test and avoid the likes of granites and rhyolites to skip quartz and feldspar. Currently in my possession some rocks carry more DS2-tested crystals with the density hovering between 2.59 and 2.68, which is above the average lamproite density (2.585 +/- 0.125). Hopefully, the amount of dissolved lamproite-associated minerals would be above the average and make it count in the PH test. Any other things to note?

14th Jan 2020 13:15 UTCPaul Brandes Manager

Frank brings up some very valid points here, Dan, the most important is to have it tested analytically because you're trying so hard for it to be lamproite (which it isnt) that no amount of internet assistance is going to convince you otherwise. So please have it professionally analysed and let us know the results.

14th Jan 2020 14:11 UTCPeter Nancarrow Expert


Your rock really doesn't look like a lamproite anyway, but for the identification method you have in mind, it's not just a matter of avoiding rocks with quartz and feldspar! Very few rock-forming minerals (except for those forming evaporites) are significantly soluble in water, so getting them into solution for any wet chemical analysis involves dissolution in a concentrated acid, perhaps HCl for carbonates, but for most silicate minerals (including all the major constituent minerals of lamproites - viz. phlogopite, richterite, olivine, diopside, sanidine and leucite) [ref. BGS], HF (hydrofluoric acid) is used.

Apart from the fact that the use of HF requires specialised lab equipment and rigorous safety procedures, such a procedure does of course render any question of being able to determine the original "acidity" of the rock (in terms of your suggestion of measuring the pH of a solution of that rock's minerals) completely meaningless.

So, to answer the question in your OP "Does it make sense to grind or ground a lamproite and measure its solution's acidity to test whether it is ultrabasic first?", the simple answer is "No"

Pete N.

Ref: British Geological Survey rock classification scheme [https://www.bgs.ac.uk/bgsrcs/rcs_details.cfm?code=LMPT]

14th Jan 2020 15:14 UTCDan Chang

Paul and Peter,

What do you think the rock and the crystal/stone look like with all the provided info? Why rule out lamproite and diamond?

I'm not so certain what it is, so I need to run some more preliminary tests before sending them to professionals because there are many collected rocks. And I am counting the coinage before I can sell some diamonds. With that said, having more knowledge and test skills in hand is always better. Am I right?

14th Jan 2020 17:57 UTCLouis Zulli

Additional well-focused images of the host rock might be valuable.

15th Jan 2020 02:39 UTCDan Chang

Louis, take a closer look here.

15th Jan 2020 02:41 UTCDan Chang

45X microscopic view of the crystal.

15th Jan 2020 11:56 UTCLouis Zulli

The rock looks like an iron-stained pegmatite to me. But I'm an amateur.

15th Jan 2020 14:36 UTCDan Chang

Louis, I don't blame you, amateur or not; many rocks just look similar. Any input from someone with petrography and crystallography experiences will help.

Take a look at this catalog of "Mantle Rocks, Kimberlite, ...".

Don't you agree the first rock picture in that page looks like mine? But, let's not judge a rock by its appearance; instead let's find a way to preliminarily test it.

14th Jan 2020 17:50 UTCGeorg Graf

Hi Dan Chang,

there are reports of people, having discovered occasionally a mineral deposit, explored it, got the right to exploit it, founded a mine and finally became very, very rich. Yes, that happened. But this is not a plan for man´´ s life!

If you want to become very, very rich, work very, very hard. Or do business at the stock exchange. (Can also be hard work.)

By the way: Your rock looks quite interesting. (Maybe a kind of marble?)

Kind regards, Georg

15th Jan 2020 02:53 UTCDan Chang

Do you have your life planned out? To me, it's more like give and take. When life gives you lemons, make lemonade! At this stage, I still try to test if I got some lamproites.

15th Jan 2020 00:13 UTCDoug Daniels

And, all of us forgot to ask - where was this specimen found?

15th Jan 2020 02:56 UTCDan Chang

island arc subduction zone

15th Jan 2020 14:55 UTCDan Chang

So far, there are different opinions on the identity of the rock. But, if you take all provided info(e.g., thermal conductivity, hardness, hydrophobia, rock density) into consideration, there is no other rock/crystal profile fits better than lamproite/diamond. Am I right?

Since no one can argue theoratically ultrabasic rock's solution tends to be more basic(PH > 7), I plan to move on bearing in mind it is not complete and full of variables and might not be accurate. But, sometimes even professional tests can go wrong for a wide variety of reasons. Don't you agree?

15th Jan 2020 16:35 UTCFrank K. Mazdab Manager

Dan Chang  ✉️

So far, there are different opinions on the identity of the rock. But, if you take all provided info(e.g., thermal conductivity, hardness, hydrophobia, rock density) into consideration, there is no other rock/crystal profile fits better than lamproite/diamond. Am I right?

Since no one can argue theoratically ultrabasic rock's solution tends to be more basic(PH > 7), I plan to move on bearing in mind it is not complete and full of variables and might not be accurate. But, sometimes even professional tests can go wrong for a wide variety of reasons. Don't you agree?
 No and no... several people have tried to explain why this won't work (clearly not successfully), but your mind is obviously made up and you already know you're going to get the answer you want to get... convenient how stuff like that always works out that way, huh? I'm going to close this thread for now because this isn't being productive for anyone anymore.  But if in the future you decide to get some professional testing done on your rock, feel free to report back your findings (but somehow I'm guessing you won't be doing that).  Good Luck!
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