FMF - Friends of Minerals Forum, discussion and message board

[Eduardoo]

Besides hardness, SG, HCl tests, streak, color, luster, and similar, what chemical analysis are available to the amateur mineralogist?

By available I mean analysis that do not cost a fortune and can reasonably be done at home.

Would you please provide some tips or direct me to some relevant source?

Thank you very much.

Eduardo.

[Paul S]

You can easily test for solubility, using different kinds of solvents, including a variety of acids.

If a mineral is soluble, you can see if it forms a precipitate if a chemical is added to the solution. Whether is forms a precipitate or not will show you with what chemical you are dealing.

Reactions can sometimes be seen when one chemical is added to another. There are too many possibilities to sum them all up, but if you think you know what chemical your mineral is, you can easily verify or disqualify it this way.

Flame colour tests can be helpful, but it is not always easy getting a good result. This test can show you what ions are present. If there are many different ones present you will not get a good result, but if there is one type of ion present in abundance, you will get a clear colour to identify it with.

And don’t forget smell as a chemical test. I don’t have a list of smells that belong to a mineral, but the smell of rotten eggs points to sulphur bearing minerals.

[David Von Bargen]

The Mineralogical Record published a book "Mineral Identification: A Practical Guide for the Amateur Mineralogist" — by Donald B. Peck that is an excellent guide to tests that can be done at home.

[Jordi Fabre]

And Eudardoo, as it seems to be that you can read Spanish language you can also visit this thread in the Spanish Forum -> https://www.foro-minerales.com/forum/viewtopic.php?t=154 where you will find a lot of basic information.

[Eduardoo]

Gracias amigos.

[Luiz Menezes]

Another interesting physical property that you can investigate is fluorescence; you need to buy an ultraviolet lamp, designed for use for minerals (with a short-wave an a long-wave source); it is normally not a conclusive test, but it can help to identify the presence of different phases in a non-crystallized specimen, and can be an important additional information, on many cases.

Can any of our friends at the Forum recommend me and Eduardoo some bibliography about a good database on fluorescent minerals?

Luiz

[Antonio Alcaide]

Hi all,

Luiz, you can find links to sites about fluorescent minerals here at this Forum

https://www.mineral-forum.com/message-board/viewtopic.php?p=9198#9198

and at the Spanish Forum

https://www.foro-minerales.com/forum/viewtopic.php?p=34224#34224

Best regards

[Gerhard Niklasch]

Indeed fluorescence can be immensely useful - not least in spotting that something unexpected is present on or in a specimen in the first place, which may be not at all conspicuous under visible light! I've made a habit of holding each and every new acquisition under the UV lamp however unlikely it may be, and I've had many surprises.

(NB short-wave vs. long-wave UV makes a difference: Ideally, get a lamp which is capable of providing either.)

The difficulty in using this as a diagnostic, though, is that only a minority of minerals (such as Scheelite) are intrinsically fluorescent. Many more (Fluorite, Calcite, Apatite,....) fluoresce due to impurities in trace amounts, and thus their response to UV can be quite different from one locality to another - sometimes it varies even from one zone to another in one and the same small crystal.

For an example where it's useful and usefully documented: The listing of minerals in the great, lavishly illustrated Långban book (D. Holtstam and J. Langhof, eds., 1999) goes to great lengths in pointing out fluorescence, which helps to recognize some of the many species occurring there which are otherwise hard to distinguish from other species. These hints may carry over, taken with a grain of salt, to other localities in the vicinity (Harstigen, Jakobsberg), and with a large dose of salt to other deposits of a broadly similar geochemistry (e.g. the Franklin district in New Jersey), but they won't necessarily generalize to material from elsewhere on the planet.

For a counterexample, look up Zincite on mindat. (In that case, the behavior varies drastically already within the Franklin district!)

Cheers, Gerhard

[bugrock]

Regarding UV response,

Having a SW and LW combined lamp works well for many specimens but sometime after purchase of that UV arrangement I picked up a MW lamp since in the fluorescent collecting sphere there are some specimens known to show better response in MW.

I also shine many pieces just to see what happens. What has been interesting is that for those minerals that are know for their SW response (maganocalcite is an example) the MW lamp very frequently shows more impressive, brighter fluorescence. This happened so often that I began to think that my MW lamp was simply putting out more light, an amplitude response rather than one of wavelength. Yet some rocks show the best response in SW, are weak in MW and little to nothing in LW. Recent lowly example I tried was an artifact rock, slag from old iron mines. Large amounts of this material wash up on some of the beaches of Lake Superior where it was dumped for many years. This bubbly/glassy material shows response in most pieces, great in SW...yellow to orange in many pieces, much weaker but same color in MW and little to nothing in LW.
Minority of pieces (20-30%) show no response.

For those interested in fluorescent minerals as a collectable group would advise a set up that can deliver all three wavelength ranges. For those who are just curious about how specimens respond a three wavelength unit (SW/MW/LW) is not a bad idea either. MW often gives improved response over SW.

[Paul S]

I came upon another way of testing minerals. It's rather simple; you just have to use a multi-meter. All metallic minerals (and graphite) conduct electricity very well. This can distinguish them from minerals that look like metallic minerals but are actually sulfides or oxides and don't conduct electricity very well.

You can measure the conductance by measuring the resistance of the material using the multi-meter. Conductance = 1/Resistance.

The value of the conductance will depend on the purity and the presence of fractures/disturbances in the mineral, but can give a distinction between different minerals.

[Gerhard Niklasch]

[Ed Huskinson]

Oiga tocayo!!! A simple test to distinguish chrysocolla from other copper oxides (turquoise, generally) is to touch your tongue to the specimen in question. Chrysocolla sticks to your tongue. Azurite, malachite and turquoise do not. Quick and easy, and a test used by geologists throughout the southwestern US, particularly those of us who have worked in copper exploration.

Hope this helps.

Ed in Kingman

[Luiz Menezes]

Muchas gracias, Antônio.

Luiz

[Eduardoo]

Hi Ed (tocayo).

I´ve been sucking the thing to dead because I really want to know what it is, but to no avail.

Of course we know in Spanish that “baba de mudo no pega” (Maybe Jordi, who speaks better English can help translate that).

I still thing the best candidate is Chrysocolla.

[Paul S]

Ed, thank you very much for that interesting test you posted. I tested it on a piece of what I thought to be malachite. It turned out to be chrysocolla. I had not found an easy test yet to distinguish between closely related copper carbonates, but this one worked! I did feel a bit weird licking my specimen. I made sure no one was watching ;-)