Wednesday, September 10, 2008

Five Minerals (or more?) on a Cold, Rainy Day

It's been a cold day at the mine. All mapping geologists came in from the field to work on their maps and get out of the rain, and the drill rig took longer to move than usual because of the mud accumulating on the roads.

It's been the kind of day where it would be good to stay inside, sit around a fire, drink some hot tea or hot chocolate, and work on photos, blog posts, or geoblog memes. I was at work, however, doing indoor things on a day when outdoor things had been planned.

I've been ruminating a bit about what minerals are most important, and I think that if limiting the number to 5, I'd have to choose quartz, calcite, clays ... and then I get stuck. Yes, pyrite sounds like a good one, it's fairly common and occurs in at lot of different settings. Iron oxide minerals (could I lump all of them together including the ones that aren't strictly crystalline?) are also prevalent around the earth's crust (and at depth to a certain point at least) - they could potentially include goethite, hematite, magnetite, and the junk-all, non-mineral limonite.

Olivine and serpentine are obviously important; olivine making up a good portion of the mantle (and also being one of the rock forming minerals on Bowen's Reaction Series), and serpentine being an alteration product of olivine that we see in places on the surface, places throughout California, for example. Olivine is not so abundant on the earth's surface, however, so perhaps wouldn't be as important for non-geologists to know.

Ice is certainly a mineral when crystalline, and in its many forms it covers a large portion of the earth's surface, at least presently, and also occurs as crystals way up in the atmosphere, forming those wonderfully wispy cirrus clouds and causing atmospheric features like circles 'round the sun. As a mineral, however, I'm not sure that it would be important for people to know it that way - most people know about ice, and know its chemical composition without knowing that it's a mineral, at least when crystalline.

My Top Five would have to be:
1. Quartz
2. Calcite
3. Clay minerals
4. Iron oxides (goethite/limonite, hematite, magnetite)
5. Olivine

So then I'd move on to what are really the most important minerals for people to know, and my list would first start with all the minerals on Bowen's Reaction Series: the (igneous) rock forming minerals, which could be listed as: olivine, pyroxenes, amphiboles including hornblende, micas including biotite and muscovite, feldspars including plagioclase and orthoclase, and quartz.

And then I'd have to add other important rock forming minerals such as calcite and dolomite. I'd add the clay minerals especially kaolinite and montmorillonite (which would include the clay mixture, bentonite), the three iron oxides goethite (commonly called limonite), hematite, and magnetite, the sulfide pyrite, and a few other minerals such as barite, gypsum, fluorite, and halite (common salt).

Possibly I'd add minerals such as the different asbestiform minerals - chrysotile (the asbestiform variety of serpentine), crocidolite (the asbestiform variety of riebeckite), amosite (the asbestiform variety of cummingtonite-grunerite), anthophyllite (sometimes asbestiform), actinolite (sometimes asbestiform), and tremolite (sometimes asbestiform). [I would argue at least for chrysotile and tremolite, and at least the knowledge that there are indeed more than one kind of asbestos, and that asbestos is a junk or industrial term, not a mineral term.]

Other minerals it might be good to know would be a couple kinds of uranium minerals, such as carnotite, autinite, and uraninite [I personally like carnotite and autinite, they are kind of pretty]. And everyone should know molybdenite and graphite. I think that many people know a few gemstone minerals, so add in corundum, because of its industrial uses, diamond, opal, turquoise, and garnet [those are some of my biases; I also like malachite, the jade minerals jadeite and nephrite, and lazurite]. Most people also know or have seen gold, silver, native copper, and native mercury. Most other elements are rarely found in pure form in nature.

This list of mine so far includes very few sulfides, which is really a travesty: I'd have to add cinnabar, stibnite, realgar, orpiment, galena, sphalerite, and chalcopyrite.

And zeolites are important for various reasons, for example clinoptilolite and erionite, which both occur in Nevada and on the Nevada Test Site. And that's more than 50 minerals! So I'll add in a personal favorite, a chromium mica - should it be mariposite or fuchsite?

The Top 50 List:
calcite: a carbonate mineral
carnotite: a uranium mineral
chalcopyrite: a copper sulfide
chrysotile: the asbestiform variety of serpentine
cinnabar: a mercury sulfide
copper (native)
dolomite: a carbonate mineral
galena: a lead sulfide
garnet: a whole group of garnet minerals
goethite (or limonite): an iron oxide mineral
gold (native)
hematite: an iron oxide mineral
hornblende: an amphibole group mineral
kaolinite: a clay mineral
magnetite: an iron oxide mineral
mariposite: a chromium mica
mercury (native)
molybdenite: a molybdenum sulfide
montmorillonite: a clay mineral, often found in bentonite
muscovite: a mica
orthoclase: a feldspar
plagioclase: a feldspar
pyroxene: another mineral group
pyrtite: an iron sulfide (fool's gold)
sphalerite: a zinc-iron sulfide
sulfur (native)
tremolite: sometimes asbestiform
zeolites: a mineral group

And then there would be my list of favorite hydrothermal minerals! (That list would start with quartz, also.)


Anonymous said...

?epidote inlcuding zoisite and clinozoisite (surely)-this is one of my favourites especially in thin section,
zircon (dating!)
chlorite because of its significance in metamorphism

Silver Fox said...

I like all the epidote group minerals, especially piedmontite. I also really like dumortierite. Chlorite is quite common and a very important mineral, so maybe I should have just put Mica
Group as one listing.

It's an interesting exercise to try to list 50 'important' minerals and keep the list to 50 - I couldn't quite get them all the ones I *first* thought of into 50!