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Techniques for CollectorsIdentifying Those Unknowns

30th Apr 2010 16:23 UTCDonald Peck

Many of the micros I obtain from swaps or from micro symposia are already identified and the vast majority seem to be correct. But, there is the occasional misidentification; and more often an associated mineral that is not identified. Then there are those Freebie Table items that are labelled, "May contain (x), (y), or (z)."

Neil Yedlin said, "We do not identify micro minerals, we recognize them". That is fine, but I have a terrible visual memory for crystals. As a result, I have to resort to tests of some kind; first usually crystal symmetry for system and maybe class, then perhaps floatation for a ball-park density, sometimes hardness, chemical spot tests for composition, or occasionally optical for anything I can learn. Most of this assumes that there are at least one or two crystals that can be sacrificed. Sometimes I succeed in finding the species ID and often I don't.

With more than 4000 mineral species, a lot of them look very much alike. A good indicator of the problem is the number of different proposed species from a single mineral photo in the Identity Help Forum. I am curious as to the techniques that others use.

1st May 2010 16:31 UTCHenry Barwood

Hi Donald,

I was interested in your post, mostly because I do a lot of mineral ID, or at least used to. Since my move to Troy 8 years ago, I've been slowly building a home lab to provide XRD and various microscopical techniques (POL and CL notably). I'm also working on a prototype tabletop XRF that I hope to have functioning soon.

Surprisingly few mineral collectors do simple testing to ID their specimens. I find that lots of micromounters are at least familiar with some of the simpler tests. Besides visual recognition, observation of such basic things as the mineral's luster and the apparent crystal system certainly will narrow the choices for an unknown. Spot tests are feasible if you have a larger sample. I will always remember Curt Segeler's Ring Oven tests! He sent me many unknowns over the years and they all were indeed unknowns because he had examined them thoroughly before he sent them to me for XRD. Another micro enthusiast learned how to do spindle stage identification and was able to sort out most of his unknowns. The key to any of this is another Neal Yedlin admonition: Buy and read a good mineral book!

It is unfortunate that newer mineral textbooks omit the detailed "tests" sections of the older editions. Mineral collectors of today rely on SEM-EDS and XRD without understanding the potential pitfalls of such techniques. Optical examination, while not rare, is also frequently performed without the benefit of rudimentary training in optical mineralogy.

I have suggested that Mindat provide a section on simple testing of species, but it would be a rather large and time-consuming project and no one is willing to take it on.

BTW, the recent aragonite/calcite test procedure posted on Mindat is a great example of the sort of thing I'm talking about.

1st May 2010 19:15 UTCDon Saathoff Expert

Don, the tecniques you mentioned are what I've always used.....the addition of your fine book has made things move faster but I still refer to my Brush & Penfield and my USGS Bulletin 848 for petrographic microscope work.....and, of course, depending upon the supposed importance of the specimen, the last resort is EDS & XRD/XRF. It's still a favorite pastime to spend some hours in the lab working on an unknown speck of a crystal found deep in a cavity (usually by my sharp-eyed wife Cookie!).

Don S.

2nd May 2010 02:40 UTCRon Layton

I use some basic chemical tests and the tried and true blow pipe and borax bead test. My grandfather was an avid collector and left me many good books on the subject of the blow pipe. I also rely on crystal form, color, and sometimes associated minerals to narrow the ID down a bit. By the way if you are interested in blow pipe mineralogy there are quite a few good books for free download at: books on blow pipe mineralogy

2nd May 2010 04:19 UTCHenry Barwood

Hi Ron,

I started out many years ago with a simple Ward's mineral test kit that included blowpipe analysis, charcoal and plaster block analyses, and both open and closed tube analyses. That was 50 years ago and what I learned has stuck with me.

2nd May 2010 16:12 UTCDonald Peck

Henry, I would be interested in hearing more about your home lab. It sounds like you are including instrumentation that most of us do not have. How are you doing that?

I learned to use the Ring Furnace from Curt Segeler, also. I seldom use it, but it is on my shelf if I need it. It will provide more hair-line spot tests than I can use from a single micro crystal; or a dissolved streak from a streak plate.

I also learned to use the spindlestage from Curt. He was a great and generous teacher. I do not own a petrographic microscope, but I cobbled a near petrographic from a student grade biological scope. It works well enough. When it, the spindlestage, and EXCALIBR (the program developed by Don Bloss, Bob Downs, Stan Evans and others) are used together, the reduction of data is extremely easy.

Has anyone used disposable borosilicate glass culture tubes for closed tube tests? I have been using 3 x 50 mm tubes with good success. They come in packs of 500 and are not expensive. Unlike the home-made variety made from lime glass tubing, they do not melt and close up on the assay and they are long enough to get a good deposit

2nd May 2010 19:02 UTCDon Saathoff Expert

For both open & closed tube work I use a pile of glass tubing which originally held the heating elements in a large mechanized film dryer - thick-walled and ~5mm ID. I don't know if they are borosilicate but they don't collapse and it takes intense blowpipe to create a bend for open-tube.

I lucked into a copy of Brush's first work - the text-book he wrote and used at Harvard. It's not as complete as later works produced after his association w/ Penfield but the intro to blowpipe work is more thorough...a lot of footnotes quoteing Berzelious & Plattner.

I make my own charcoal from blocks of spruce cut to 1"X1"X4"....spruce seem to have a grain better than pine and holds together better.

I'm glad there are still people out there using the older techniques!!!

Don S.

2nd May 2010 19:47 UTCHenry Barwood

Hi Donald,

I monitor such sites as eBay and LabX for instrumentation. The trick is to know something about the various XRD, etc. units. I got an old Phillips XRG 2500 for $100 (it cost me $600 shipping!) and hooked it up in my shop. Since I've worked with them over the years, I know that they are fairly simple to repair. I've got mine hooked up to where the X-rays cycle through the delay circuit, but then a fuse blows. As soon as I can find the short, I should be generating (I am looking forward to some time to do so between semesters!). I also have a well stocked pantry of tubes, tube towers, spare parts, goniometers and powder cameras from both purchase and give-aways.

Just a month ago the University of Oregon dumped all their student petrographic microscopes on LabX. While I have several, I bought a nice Leitz scope with a case and all necessary plates for a whopping $50 + $20 shipping. My Luminoscope cost me $100 plus $150 for the vacuum pump. I have a good microhardness tester I've never even used that set me back $75 plus a few repairs. I build my own spectrometers.

With a little ingenuity, and some luck on the Internet sales, you can assemble a good working mineralogical lab that will not kill your budget. My biggest problem is finding the time to do the necessary repairs. I've learned not to work tired. I did this one time and now my daughter refuses to help me anymore since I vaporized a multimeter trying to trace a connection on one of the XRD units at work. Scared the you-know-what out of her!

The biggest problem with Spindle Stage is finding inexpensive oils. I have two sets, but they are out of calibration. I need a refractometer, but have not had much luck finding one in my price range. Oh well, one day. I first used EXCALIBR when it ran on a mainframe using punch cards (I know, somewhere in the Precambrian). Managed to kill the program running a sample of strengite, but that problem was corrected by the time it went to the PC's.

My department used some spare funds to buy the necessary components from AmpTek for my XRF unit. I managed to destroy the first diode and had to wait 7 months for replacement funds. Just last week, between finals, I assembled the specimen holder prototype and I'm really hoping to get everything up and running soon.

Got kind of long-winded here, but I think you see that such things are not hard to do, just time and funds consuming!

3rd May 2010 15:35 UTCDonald Peck

Henry, I wish I had your expertise. But I will borrow your practice of watching ebay. That petrographic sounds like a real steal! I have never worked with XRD, SEM or any of their relatives, so I doubt I will ever try to find those. I would probably fry my innards.

Don, that tubing sounds good, and I would guess that the price was right. A few years back I was using cheap lime-glass tubing; about a 3mm bore. It was too narrow for open tube tests, but would have been fine for closed tube work. The problem was that I often got it hot enough that the sides would begin to close in on the assay. That doesn't happen with my borosilicate culture tubes . . .and I don't have to make them.

Flame tests and bead tests used to give me a problem too. I used platinum wire set in glass handles of the type that are sold by geological supply houses. I had a prblem with the wires getting continually shorter, until there was only a nub left. Then I discovere platinum inoculation wires used by microbiologists. They are heavier,gauge, stiffer, and for some reason less expensive. Made my life a bit easier.

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