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Thread: Minerals?!

  1. #1 Minerals?! 
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    "There are 4 things that must be satisfied for a substance to be a mineral:
    (i) natural
    (ii) inorganic
    (iii) solid in crystalline form
    (iv) definite chemical composition"

    I don't fully understand (iii) and (iv).

    1) Gold is a naturally occurring inorganic substance that forms in the earth's crust. It is a solid and has a definite chemical composition. Is gold a mineral? Explain your answer. (Assume you know nothing about gold, as if it is an unknown substance that you have to determine if it is a mineral or not.) This is a question from my text book's section review.

    From the above information, gold seems to be missing something that must be satisfied to be a mineral, gold is a solid but is not mentioned to have crystalline form. For a mineral layman like me, I would predict that gold is not a mineral according to the information provided, right?

    For (iii) solid in crystalline form, is it true that a solid always has crystalline form, and a substance that has crystalline form is always a solid? If so, I would predict that gold is a mineral now since the information says that it is a solid, and this automatically satisfies the (iii) requirement. If not, gold is not a mineral...I think...

    2) For the (iv) requirement for a mineral, "definite chemical composition", what does it mean by that? I don't get it! Is concrete a mineral and why?

    3) Are rocks mixtures (not chemically united) or compounds (chemically united)?

    4) An example of a mineral with a basic structure consisting of single tetrahedra linked by atoms of other elements is ________
    (pick one of mica, olivine, quartz, or feldaspar)
    I can't tell if the answer is mica or olivine, can someone explain?

    I don't understand! Can someone who know "minerals" explain? Thanks a lot! :wink:


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  3. #2  
    Universal Mind John Galt's Avatar
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    Ah, Kingwinner, bless your heart. You are causing me to re-establish neuronal connections that have not fired for decades.

    I don't like the definitions you have been given for minerals. I'm not saying they are wrong, but they certainly don't feel right to me, especially iii) and iv). That might be why you are having trouble with them.

    For example, from a site chosen almost at random (http://webmineral.com/crystal/Amorph...Crystals.shtml) we are presented with a table of 32 Minerals with Amorphous - No Crystal Structure. Setting aside the abominable grammar it is clear from this site (and virtually any mineralogy site you care to visit) that a crystalline structure is not a pre-requisite for a mineral.

    Anyone who thinks minerals have a definite chemical composition has not spent any time considering the mineralogy of the clay minerals. We can give idealised compositions for particular clays, but the reality is quite different in detail.

    That said, gold is a mineral, in terms of the definitions you have been given. I am puzzled Kinwinner, why you have not investigated this a little more closely using google. You say gold is 'not mentioned to have a crystalline structure'. Where is it not mentioned?!! Just google gold "crystal structure", to turn up 442,000 hits. The second hit notes "The following web sites give a lot of info on gold in general, and the crystal
    structure in particular: ..."


    Crystaline implies regular structure of fairly uniform composition. Gold delivers that.

    I don't understand your question - "what is meant by a definite chemical composition". Concrete is not a mineral because it is not natural.

    You tell me what rocks are? Come on Kingwinner, start thinking and stop trying to learn by rote. Are the individual minerals chemically linked to each other in a fundamental way within rocks? Does this seem likely? If they are linked in a fundamental way, where does one mineral end and another begin? Set down your thoughts onthis point.


    Olivine consists of single tetrahedra linked, generally, by iron or magnesium.
    Micas are sheet silicates, with the tetahedra linked to each other, with other elements sitting between the sheets.


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  4. #3  
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    Quote Originally Posted by Ophiolite
    Ah, Kingwinner, bless your heart. You are causing me to re-establish neuronal connections that have not fired for decades.

    I don't like the definitions you have been given for minerals. I'm not saying they are wrong, but they certainly don't feel right to me, especially iii) and iv). That might be why you are having trouble with them.

    For example, from a site chosen almost at random (http://webmineral.com/crystal/Amorph...Crystals.shtml) we are presented with a table of 32 Minerals with Amorphous - No Crystal Structure. Setting aside the abominable grammar it is clear from this site (and virtually any mineralogy site you care to visit) that a crystalline structure is not a pre-requisite for a mineral.

    Anyone who thinks minerals have a definite chemical composition has not spent any time considering the mineralogy of the clay minerals. We can give idealised compositions for particular clays, but the reality is quite different in detail.

    That said, gold is a mineral, in terms of the definitions you have been given. I am puzzled Kinwinner, why you have not investigated this a little more closely using google. You say gold is 'not mentioned to have a crystalline structure'. Where is it not mentioned?!! Just google gold "crystal structure", to turn up 442,000 hits. The second hit notes "The following web sites give a lot of info on gold in general, and the crystal
    structure in particular: ..."


    Crystaline implies regular structure of fairly uniform composition. Gold delivers that.

    I don't understand your question - "what is meant by a definite chemical composition". Concrete is not a mineral because it is not natural.

    You tell me what rocks are? Come on Kingwinner, start thinking and stop trying to learn by rote. Are the individual minerals chemically linked to each other in a fundamental way within rocks? Does this seem likely? If they are linked in a fundamental way, where does one mineral end and another begin? Set down your thoughts onthis point.


    Olivine consists of single tetrahedra linked, generally, by iron or magnesium.
    Micas are sheet silicates, with the tetahedra linked to each other, with other elements sitting between the sheets.
    I searched the internet and the definitions of a mineral are the same...so I guess this definition is a pretty good fit for high school uses...omiting some exceptions

    1) I think you do not really get what I mean, the focus is on the information given, not the gold!
    Lets reword the question and put in this way:
    Substance X is a naturally occurring inorganic substance that forms in the earth's crust. It is a solid and has a definite chemical composition. Is Substance X a mineral?

    Would you consider this substance X as a mineral based on the given information? (no information about whether it has crystalline form or not...however we know that it is a solid, is that enough for it to be a mineral?)

    2) "definite chemical composition" means it can be representated by a chemical formula, I have found out! Concrete can be formed by any proportion, thus no definite chemical compostion

    3) I guess rocks are both mixture and compound! But are rocks homogeneous mixtures (solution) or heterogeneous mixtures?
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