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Author Topic:   Introduction To Geology
roxrkool
Member (Idle past 1094 days)
Posts: 1493
From: Nevada
Joined: 03-23-2003


(1)
Message 28 of 293 (634898)
09-24-2011 4:01 PM
Reply to: Message 27 by Dr Adequate
09-23-2011 4:25 PM


Re: Minerals and rocks: definitions
Well done.

I'll add a few things...

"Rock crystal" is not a term I would ever use as a geologist and I doubt any other geologist (at least in the States) would know what exactly I was referring to if I used it. I would use, "quartz crystals." We tend to use terms that are exact/descriptive rather than ambiguous.

A rock can also be composed of clay particles as well as organic matter: shale and coal, respectively.

As far as solid solutions go, we have specific mineral names for the various phases of a solid solution series. For example, using your olivine example, forsterite is the Mg-rich end-member and fayalite the Fe-rich end-member of the olivine solid solution series. Both minerals are olivines, but geologists like to distinguish between them for a variety of reasons. Namely, compositions of minerals tell us what sorts of conditions exististed when they formed. An abundance of Mg-rich minerals in igneous intrusions usually suggests that the melt was hotter and generally more primitive (i.e., less evolved/differentiated) than one that contains an abundance of Fe-rich minerals (i.e., more evolved/differentiated).


This message is a reply to:
 Message 27 by Dr Adequate, posted 09-23-2011 4:25 PM Dr Adequate has responded

Replies to this message:
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roxrkool
Member (Idle past 1094 days)
Posts: 1493
From: Nevada
Joined: 03-23-2003


Message 30 of 293 (634944)
09-25-2011 12:25 AM
Reply to: Message 29 by Dr Adequate
09-24-2011 9:03 PM


Re: Minerals and rocks: definitions
I've not heard or read anything regarding organic material being classified as a mineraloid, but that can change or has changed(?). Clays, such as illite, chlorite, etc. are minerals, but "clay" is also a particle size. So clay minerals, as well as clay-sized particles (of other minerals), comprise shale. (Just an FYI for the readers. )

Iron, the metal, may have a higher melting point than magnesium metal, but Mg-rich forsterite is a far more stable mineral under higher temps and pressures (as present in the mantle) than the Fe-rich fayalite. Therefore, forsterite will crystallize first from higher temp ultramafic/mafic melts, rather than fayalite.


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roxrkool
Member (Idle past 1094 days)
Posts: 1493
From: Nevada
Joined: 03-23-2003


Message 32 of 293 (635058)
09-26-2011 8:35 AM
Reply to: Message 31 by Dr Adequate
09-26-2011 12:31 AM


Re: Minerals and rocks: definitions
Ah yes, I see the inclusion of organic material. Hmmmm... not sure I agree, but not really worth arguing it. As for the clays, I was simply elaborating a bit for the readers. Not everyone knows clays can also be minerals.
This message is a reply to:
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roxrkool
Member (Idle past 1094 days)
Posts: 1493
From: Nevada
Joined: 03-23-2003


Message 180 of 293 (675386)
10-10-2012 8:58 PM
Reply to: Message 179 by Pressie
10-10-2012 12:40 AM


Re: Petrophysics
Geology can be pretty "touchy feely," which is what drives the engineers crazy. Occasionally, there just isn't enough evidence to be sure, as you very well know, so we have to go with our gut. The longer you've been a geologist and the more rocks you've seen, the better your chances of being closer to the truth.

I'm modeling an ore deposit right now and I can tell you I'm digitizing a lot of touchy feely lines at the moment.

Edited by roxrkool, : No reason given.

Edited by roxrkool, : No reason given.


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