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Trouble with identification of minerals

  1. Feb 11, 2017 #1
    Lately I'm learning how to identify the most common rock-forming minerals, but I have some doubts about it. First of all, how can I distinguish between massive minerals and rocks? Second thing, a massive mineral from what I understood, has an internal order (so it's not amorphous), but that does it mean that the piece I get is a big single crystal (or a piece of a bigger crystal), or that it just has no crystals in it? Because often I noticed that I can see cleavage plans on a massive piece of mineral as well.
    Thanks in advance :wink:
     
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  3. Feb 12, 2017 #2

    davenn

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    sometimes, but not always .... it doesn't really tell me what you mean by the term massive mineral ... not a term I'm familiar with
    and I have been rock and mineral collecting for 50 years

    A rock is just a term for any lump of material out of the ground ...
    first we classify it as metamorphic, sedimentary or igneous
    then going on from there we see if we can identify minerals in it

    the minerals may be easily identifiable by eye or small magnifier. Others samples the individual minerals may be identified
    when thin section slides are made from the sample. More difficult times we may use methods such as XRD ... X-Ray Diffraction
     
  4. Feb 12, 2017 #3

    davenn

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    Identifying minerals by eye takes a lot of time and practice
    minerals come in their own specific crystal form, hardness, streak, lustre and colour and rarely vary from, what type of rock they are coming from, eg. metamorphic, sedimentary or igneous and getting to learn those differences is what helps you identify them.
    You start with the common ones, quartz, and some of it's family ... eg. agate and chalcedony both varieties which are often found in an amorphous state

    eg .....
    if you have a silver/grey metallic looking and cubic crystal form mineral it is a high probability that it is Galena (PbS = Lead Sulphide)
    Calcite is usually easily recognisable mainly due to its colour ( usually lack of) and it's crystal form

    as time goes by, you add more to the list of ones that you rarely misidentify
    I can readily identify 40 to 50 minerals at a glance and a bunch more with a closer study

    Other minerals are radio-active, others are fluorescent under UV light giving off specific colours under UV

    Many years ago, when I was doing geology at university I was able to make use of the trickier methods of mineral ID
    Thin section, XRD and XRF

    Thin section .... Petrology
    this one is an awesome skill to become familiar with .... just preparing the slides is an art form in itself
    commonly used for igneous and metamorphic rocks where there may be no easily visually distinguishable minerals .... their presence becomes very obvious in a thin section slide under a microscope> Again, it takes time and practice ( experience) to learn to identify the minerals in the thin section you are looking at
    http://www.bing.com/search?q=manual+thin+section+slide+preparation&FORM=HDRSC1
    http://www.bing.com/images/search?q...thin+section+slides+of+rock+samples&FORM=IGRE
    http://www.bing.com/search?q=petrol...8-9&sk=&cvid=89339CF4E8CA43CEBB285658C64D0A9B

    XRD .... X-Ray Diffraction
    http://www.bing.com/search?q=XRD+mi...earchBox&FORM=IENTTR&conversationid=&pc=EUPP_

    XRF ..... X-Ray Flourescence
    http://www.bing.com/search?q=XRF+mi...-26&sk=&cvid=7600D0D1FE7D44E98F9F0A8D4F007D24


    hope the last two posts help you
    feel free to ask other questions


    Dave
     
  5. Feb 12, 2017 #4

    First of all, thank you very much for all this information! Here's an example of what I mean with massive mineral (I learned this term at university, and it's used to define a mineral with no crystal structure visible). [​IMG] This a Kaolinite sample, but if I look at it for the fist time, I'd call it rock, because it hasn't got any form of crystals in it, at least they're not visible. So I was wondering how I distinguish between a massive, earthy mineral and a rock, with only macroscopic analysis?
    Also, I'm a little familiar now with some of the analysis techniques that you mentioned, and I'm capable (but I have very small experience) of using a polarizing microscope and observing the optical sign, and some features of a thin section.
    Now, that you mentioned that you are a mineral collector, I must admit that I'm really glad of knowing that, because I have a great passion for minerals, and I'm only doing a single semester course about mineralogy, and I have great fear that with only that little experience that it gave me, I won't be able to realize my little dream of having a collection, studying only by myself. Because I realized, that in order to understand deeply the features of a mineral and being able to distinguish between them, I must have a direct contact with them, and it is also important the presence of an instructor that teaches me how to do that. But I won't have someone to teach no more, because the course came to an end, and I can only learn by myself from now on. So, I was wondering if you have any advice for me about learning by myself without any professional telling me things, if it is really possible, and if there are any sources (books, or anything else) that can help me in that. I acknowledged also that when it comes to buying minerals, unfortunately sometimes sellers can sell "fake" minerals (like synthetic minerals or a kind that looks like another one and so on...), and so I must be capable of recognizing real pieces from others and this is also another difficulty for me that I'm just starting in this field. So any advice, would be gold for me.
    Anyway, even if you can't help me in this, I thank you for your attention and your answers.
     
  6. Feb 12, 2017 #5
    Sorry here's the kaolinite sample
     

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  7. Feb 12, 2017 #6

    jim mcnamara

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    Whoops. Kaolinite occurs as a weathering, secondary mineral in igneous, sedimentary, and metamorphic formations. Soils may contain kaolin as part of the clay particle fraction of the soil. It is soft, you can usually scrape it with your fingernail. It crumbles, too. If you soak it, it becomes cuttable with a knife - not many minerals do that. It is also similar to several related minerals, that have the same chemical formula.

    So it kind of breaks some of the rules of thumb @davenn presented earlier. ( This is one of the reasons mineral identification is occasionally difficult. ) Kaolinite also has the sometimes confusing, but really nifty and useful trait of changing structure when exposed to heat. e.g., making high quality clayware when heated in a kiln.

    You picked a bad starting choice for developing sets of rules for distinguishing minerals.

    http://www.minerals.net/mineral/kaolinite.aspx
     
    Last edited: Feb 12, 2017
  8. Feb 12, 2017 #7
    Yes, I know is not a good choice, but the point is that I had problems with it and with other minerals with this "massive" or earthy shape. I'll try to give another two examples, like this piece of magnetite, and this sample of pyroxene. Both of them doesn't have crystals (at least not visible), and are massive, so what I don't understand is how I distinguish between a rock and a mineral that hasn't got any crystals, and it is opaque? For example if I found on a excursion pieces like that, how I can say only looking at them, if they are minerals or common pieces of rocks? Anyway I must say that I don't know much about rocks, I know only about minerals, and when the sample has crystals, or it has metallic luster (or even a non metallic luster and it's transparent or translucent) it's relatively simple to identify it by hardness, streak and cleavage, but when it comes to this samples with earthy luster I'm not even sure that it can be a mineral.
    Anyway thanks for your response :)
     

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  9. Feb 12, 2017 #8

    jim mcnamara

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    I see black crystals in the magnetite. Think of crystals that and ant could wear as jewelry, not the gigantic quartz things you see in mineral stores.
    They are there as inclusions. An inclusion is a different mineral from the "main background", and can be a small crystal. I'm not helping. I cannot do much for you from here on.

    If you really like minerals, try the library. There is a lot involved in identifying minerals. Check out a book with a title similar to 'Field Guide to Minerals'. These books are written for specific geographic areas. For non-geologists.

    I happen to live in a place that geologists from around the world come to investigate. The field guides here are thick with the array of extant minerals.

    [offtopic]
    We have a series called 'Roadside Geology of [ Central, Eastern,and so on...] New Mexico. These things are great for neophytes! if there is one for your area. We even have a Rockhound State Park, which I think may be unique. You can keep whatever you find there. As you can tell I've been there many times.
    [/offtopic]

    Stuff you will need:
    Frequently you need to break open a specimen because the outer layer is covered with weathered rock material - like your friend kaolinite. A hammer and good eye protection works for this. You also will need a small field kit with things like a copper coin, a carborundum nail file, etc., as explained in the books.
     
  10. Feb 12, 2017 #9

    davenn

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    your definition isn't really good
    a mineral can be defined as a rock sample, a rock is a mineral or set of minerals ... generally finer grained <-- that is probably a better definition
    you need to change your idea of that definition and broaden it a bit
    As I said earlier the term rock is just a general description for any lump of material that comes out of the ground

    why not ?
    I started collecting when I was around 7 or 8 yrs old ... As I said earlier, I have been doing so for some 50 years. Just take every opportunity when you are travelling around to pick up samples and take them home for study and classification
    There are a number of books available for identifying rocks, minerals and fossils

    Dave
     
    Last edited: Feb 12, 2017
  11. Feb 12, 2017 #10
    Well this is a good idea, I didn't think of that. I live in Italy, even if there are a lot of different types of minerals common for each region, there's no comparing with New Mexico that is like a mine for mineralogy passionates, you're very lucky! Anyway, I already have my little field kit, and I'm looking forward to search for some places like the ones you mentioned. Thank you very much!
     
  12. Feb 12, 2017 #11
    Alright, maybe I have to understand better the differences, I'll check out better this terms and their meaning.
    For now I have only one book for minerals, that is "introduction to rock-forming minerals - Deer, Zussman", that is helping me a little, but I'm thinking of searching for more practical books, with examples and advices.
    Anyway thank you very much for the info and for you time :)
     
  13. Feb 12, 2017 #12

    davenn

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    Not sure where the New Mexico reference came from ? .... I live in Sydney, Australia ... grew up in New Zealand ... have been through the state of New Mexico in the USA a couple of times, mainly for storm chasing

    as I kid, I would pick up various coloured stones on the road side, the beach etc to take home ... I still have a habit of occasionally stopping at those and other places. Places where the road cuts through banks and hillsides are great for collecting, specially if they are reasonably fresh cuts. You get access to all sorts of rock and mineral types :smile:

    handbooks like this are ones you need to get ....
    ones that have clear pictures of all the samples and full descriptions ( all their properties) of each of those samples
    http://geology.com/store/geology-books/simon-and-schusters-guide-to-rocks-and-minerals.shtml

    this helps immensely when trying to identify samples .... I usually use a yellow highliter pen to highlite the samples I have in my collection
    Warning ... this hobby can become VERY addictive over the years :wink:

    Not all the samples in my collection are ones I have personally collected, some collected, some purchased <-- specially overseas samples, some swapped with other collectors, some given to me by friends that work in mines etc

    It doesn't really matter what you start with ... rock samples of igneous, metamorphic and sedimentary ones or the other way just with nice mineral samples. The REALLY IMPORTANT thing is to start your catalogging right at the start with ALL the info on how you obtained the sample and where it came from


    Dave
     
    Last edited: Feb 12, 2017
  14. Feb 12, 2017 #13
    The New Mexico reference was for Jim Mcnamara ;) However, wow storm chasing, that's very interesting!
    I would like, as well, to start picking up some samples to study at home, when I go on a trip, but I'm starting a little bit later than you (I'm 22) because even if I liked this field since I was younger, I never thought of taking rocks and observing them, because I always thought I wouldn't be capable of understanding anything about them (I'm studying mineralogy only now at university as an optional course). And I realize now how many chances I've lost for that, every time I went to volcanic lakes :H At least I will appreciate these places more now :smile:
     
  15. Feb 12, 2017 #14

    davenn

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    ahhh OK ... just realised you had quoted him and not me ... my error .. no problem

    mite get to Italy and some other parts of Europe one day ... maybe long way and expensive to get there from Australia
    you have lots of volcanic rocks in Italy and Sicily region ... I would love to video some eruptions at Mt Etna


    awesome on the studies ... you may find you also develop an interest in earthquakes and their causes
    I have my own seismograph at home, have been recording earthquakes since the early 1990's

    my live seismograms -- update every 5 minutes
    http://www.sydneystormcity.com/seismograms.htm

    background on my station
    http://www.sydneystormcity.com/g_phones.htm


    that happens and yes you will .... once you start learning about tectonics and landforms, you never view a landscape the same way again
    please keep in touch :smile:



    D
     
  16. Feb 12, 2017 #15
    I'm really sorry, I realized I didn't read all your previous response (page lag), and all your precious advices... the book you linked seems very helpful, I think I will order it as soon as possible, thanks! Anyway I really admire all you passion in this field, and for sure I'll check the links you gave me :) I suggest you, whenever you have the possibility, to come and visit Italy, it is a must for a geology passionate and it has also really really wonderful places to visit, however I am aware that is very far away from Australia!
    I'm really looking forward to be addicted to mineralogy :biggrin: And I thank you again for your helpful advices, I really appreciate it!
    Even if geology and earth sciences aren't my main field, I find some natural phenomena in particular (especially earthquakes) beyond fascinating.
     
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