Monday, January 3, 2011

A Follow-up to the Mineral Videos [Original Post Date 01/04/09]

on minerals, just a few additional words on the subject to review clarify this issue for non-geologists (normal people). [Being on the road when those two videos were posted, I didn't have time to watch much of either, so if I repeat any of what was said, it is because what I wrote below is just part of my standard opening to the Physical Geology chapter on minerals.]

By definition, minerals are:

Naturally occurring, solid (at normal temperatures), inorganic (though they may be formed by organic processes), they have a definite chemical composition (or range), they have an orderly internal structure, and they have definite characteristics, e.g., crystal habit, cleavage, hardness, color (though color may be unreliable because of trace elements).

Minerals are important because they are the "building blocks of rocks". Most rocks are composed of two or more diffrent minerals, though there are a few rocks that are only composed of a single mineral, e.g., pure marble, pure quartzite, pure limestone...

Geology students generally learn to recognize individual minerals first, then they usually learn to recognize them in igneous rocks, as igneous rocks are the original source of most minerals, including the minerals that make up sedimentary and metamorphic rocks.

Some of the most common minerals that we come in contact with are salts - Halite (NaCl) being the most common of these and Sylvite (KCl) if you use Morton Lite Salt. There are other salts - potassium iodide (KI), etc. that are used for various reason in foods to deliver various trace elements that we need (or that enhance flavors).

Other minerals we encounter are quartz (the most common mineral on Earth), diamond (the hardest), perhaps some other gemstones, gypsum, and for anybody that still uses black-and-white camera film, some silver salts (I am clueless as to the chemistry of color film emulsions). [Sadly, IMHO, film photography is slipping further into history, which some folks will regret as digital images themselves are lost over time.]

BTW, for the beautiful crystals that some folks like to marvel over, for those nice crystals to form, they have to have "room to grow", perhaps into a fracture zone, or some other cavity or open space, or they were among the first minerals to crystallize in a cooling magma. Sometimes those growing crystals include (surround) other minerals as the crystal grows or in the case of gypsum (or other salts) in sediments associated with salt lakes, sometimes the crystals will include small rock fragments, sand grains, and other stuff.

Usually, geologists are not lucky enough to have good, well-shaped crystals for the purpose of identification. That is why we learn the other characteristics of individual minerals. There are high-tech ways of analyzing rocks, but they take time and cost money, so field geologists are still required to make a quick-and-dirty assessment of what minerals are present in a rock and uses the proportions of major minerals to define the rock itself.

[As I think of other examples, I may include them.]

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