Naked Science Forum
Non Life Sciences => Chemistry => Topic started by: katieHaylor on 14/09/2017 11:29:38
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Geoff asks:
What is a mineral? Some say it needs to be solid at room temperature and some say not.
Can you help?
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I think all common definitions of mineral require it to be solid in its natural state. But I don't agree that something has to be solid at room temperature to be considered a mineral (though that is typically a safe assumption).
My counterexample is... water ice!
In parts of our world where it is consistently below the freezing point of water, and especially on other worlds (like Europa, Enceledus and Pluto) water ice is always solid, and a very integral part of the "geology."
My understanding of the definition of mineral is:
A naturally occurring, solid substance with a well-defined composition. Some people include that it must be inorganic (meaning it contains no C-H bonds), but I'm not sure I agree with that, as it would rule out coal, amber, jet, and methane-water-clathrate (all of which are minerals in MY book). That said, I feel like a mineral should be formed through abiotic processes (even if the precursors of the mineral are biotic in origin)
To back myself up, I present:
http://www.minerals.net/mineral/ice.aspx
http://geology.com/articles/water-mineral/
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Gold, Platinum and Silver are minerals, often found as native metal due to their non-reactive nature. These metals are concentrated in veins of intruded rock and differentiated by their various melting points.
Other metals are more reactive, and usually found as oxides, sulfides, etc (apart from the occasional nickel-iron meteorite that hasn't rusted away, yet).
My temporary counterexample is: Mercury.
- Mercury is often found in the form of Cinnabar (HgS), a solid red mineral.
- There are tales of lightning strikes in Cinnabar-rich rocks which caused liquid mercury to ooze out of the rocks.
- Due to its volatility, Mercury would eventually evaporate, and due to its reactivity it would react with oxygen or sulfur to form other solid mercury compounds.
But I suggest that in the temporary state of liquid mercury, it is still a mineral, which has been produced by natural processes in the lightning strike.
See: https://en.wikipedia.org/wiki/Cinnabar
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I find it interesting that most things in science seem to require accuracy. Yet, when it comes to basic definitions, they are merely guidelines and left to one's personal interpretation.
Why should a mineral need to be solid in it's natural state? If we include solidified H2O, then why not also include solidified Co2 or solidified methane etc. They exist as a solid in their natural state on some planets. Are minerals only minerals once they are on Earth?
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I find it interesting that most things in science seem to require accuracy. Yet, when it comes to basic definitions, they are merely guidelines and left to one's personal interpretation.
Why should a mineral need to be solid in it's natural state? If we include solidified H2O, then why not also include solidified Co2 or solidified methane etc. They exist as a solid in their natural state on some planets. Are minerals only minerals once they are on Earth?
Categorizations are an aspect of human psychology. It is easier for us to think about the world by classifying objects, phenomena etc. And while it is useful, it is often flawed or superficial. Upon further inspection there are so many exceptions to the "rules."
We also get to choose which classification system we need to address different questions. My favorite example is the term "metal," which chemists use to classify over half of the periodic table (s block minus hydrogen, d block, f block, and the bottom half triangle of the p block), materials scientists use "metal" to mean any bulk material that has mobile charge carriers in the conduction band (this definition extends to a diverse array of materials, including some ceramics and even some proteins!), cosmologists use "metal" to describe any element other than hydrogen or helium, and musicians use "metal" to describe a genre of rock music based on complex riffs, virtuosic solos and high precision awesomeness.
I would certainly think of solid CO2 as a mineral on Mars or elsewhere.
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And then there is mineral water. Should that not be mineral mineral? What if you put ice in it? Mineral mineral mineral.
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Musical interlude.
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The musical interlude describes minerals as being "inorganic".
Limestone is mined commercially, for example to use in cement; Wikipedia has this to say:
Limestone is a sedimentary rock, composed mainly of skeletal fragments of marine organisms such as coral, forams and molluscs. Its major materials are the minerals calcite and aragonite, which are different crystal forms of calcium carbonate (CaCO3).
So it is derived from living things, and it is mainly composed of two forms of calcium carbonate which are both described as minerals.
So would you call limestone a mineral?
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So, science doesn't have rules, just guidelines? I guess this would allow for more flexible thinking which is necessary for progress.
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Thinking about it more, granite is a rock, which consists of many minerals.
I guess limestone is also a rock (not a mineral), which consists of many minerals. As well as Calcium Carbonate, Limestone typically also contains sand and silt deposited on the seafloor, which represent other minerals.
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AFAIK minerals refer to natural occuring compounds of misc elements. Not sure what the difference to rocks is though