While I was away, the rest of the geoblogosphere spent some time creating a list of 50 minerals to see before you die, and then ticking off which ones they've done; Dave Schumaker put together a neat tag cloud to display the results.
Intimidated by the length of this list, Callan, Kim, EffJot, Geology Happens, and Silver Fox have come up with shorter, more focused lists of the 5 minerals they would introduce to earth science n00bs. They are mostly focused on minerals that are "important" in the sense that they play significant roles in geological processes.
As a geophysicist and mostly-physical hydrogeologist, I do most of my thinking about the Earth and other planets without reference to minerals. Occasionally I need to consider them because they possess particular physical properties, like slipperiness, a tendency to flocculate, or the ability to conduct seismic waves faster in one direction than another. Usually, though, the mineralogy of a sample is a source of shiny curiosities whose significance is best interpreted by someone else.
As a geophysicist/physical hydrogeologist who impersonates a real geologist on the Internet, I am often called to reach well beyond my mineralogical expertise, usually by people who have a mystery rock in their hands. So the minerals I think are important to be familiar with are those that are (1) visible and interesting in hand samples, and (2) likely to be useful when I'm engaged in
blatant lies bluffing educated speculation.
After the jump: Five minerals that will make you sound smart.
- Quartz is everywhere. It is durable, and so makes up the bulk of sand on beaches and in sandstones. It is shiny. It sneaks in to determine important properties of non-crystalline rocks like flint or chert.
- Calcite, also known as calcium carbonate (CaCO3), is what makes up seashells. usually the first mineral to form as a precipitate from evaporating water. That limey build-up around your kitchen faucet? Mostly calcite. Strangely-shaped towers rising from a lake? Calcite. Any whiteish gunk on any surface that may have been in contact with evaporating water at some point in the past million years? Go ahead and call it calcite.
Calling something calcite will give you an excuse to perform destructive experiments! If you pour a bit of acid on some calcite, it will fizz, as the "carbonate" part of "calcium carbonate" becomes carbonic acid. So you can use mineralogy to clean your faucets: Soak a paper towel in some vinegar and wrap it around the lime. Let it sit for a bit, then wipe, and the calcite should come right off. Or you could just throw highly concentrated hydrochloric acid onto priceless marble sculptures, it's really up to you.
If acid doesn't make it fizz, well, it probably isn't calcite. But take heart! There's another mineral, dolomite, that's almost exactly like calcite except that
mosthalf of the calcium spots have been taken up by magnesium. Magnesium is right belowabove calcium on the periodic table, so they are chemically very similar elements; the only easily observable difference between the minerals calcite and dolomite is that dolomite doesn't fizz (much - it will still fizz if the surface is freshly-scratched or powdered). Switch your guess to dolomite and carry on.
- Pyroxene - again, this is actually a group of minerals. It is useful to know because non-geologists have never heard of it. You can call any random specimen "a pyroxene" and your interlocutor will be impressed. If you need extra syllables, try the subclassifications of clinopyroxene and orthopyroxene.
- Mica is important because it is shiny. Tiny flakes of mica are used to make high-end craft glitter and shimmering make-up; if you are out in a river pretending to pan for gold, you can easily rain on your companions' parades by dismissing their shiny specks as "just mica". Larger samples of mica are easy to recognize because of the distinctive "flaky pastry" cleavage.
Once again, I am cheating by listing a mineral group, instead of a particular mineral. If you insist on learning just one mica, pick muscovite (reasonably common and exceptionally flaky) or biotite (often found as a component of granitic rocks).
- A Mineral of Local Importance... this is a cop-out, I know. But while I was thinking about this list, I kept fighting a tendency to just reel off the minerals that are most likely to appear in California, where all of my serious geologic education has taken place. But there are parts of the world that aren't all giant lumps of granite and serpentine-lined fault zones. So, to really bluff your way through a mystery rock, you'll need to be familiar with at least one of the common or economically important minerals in your area.
If you're in California, I suggest serpentine. If you're elsewhere in the U.S., you might start with your state's official rock or mineral. For the rest of the world... maybe you can suggest a good one for your region in the comments?
Oh, and it can't be pyrite. Everyone already knows pyrite.
almost exactly like calcite except that most of the calcium spots have been taken up by magnesium.
Every other calcium spot has been taken up by magnesium, resulting in half calcium, half magnesium.
And dolomite does fizz if you make a fresh scratch in the surface.
I think "flocculate" is one of the funniest words in the English language. And I'm really, really excited that it is in my field! Yay! (I got really tired of it in college when all my chemistry and chem eng friends got to make all the dumb jokes about terminology. Then I took sedimentology, and I got flocculate. Woohoo!)
Oh, and it can't be pyrite. Everyone already knows pyrite.
(So why do so many people come to my office wanting to know if pyrite is gold, then? Not as many as ask whether an iron concretion is a meteorite, true, but "is this gold?" is one of the most common questions I get asked.)
NJ, SW: Thanks. See, I told you I only impersonate a geologist on the Internet!
It's not that you are impersonating a geologist. You just aren't enough of a mineral geek to be worried about the differences between R bar3 and R bar3/c as space groups...
Nevada: we have a state metal, silver (Ag); a state precious gemstone, black fire opal; and a state semi-precious gemstone, turquoise -- but not an official state mineral!
"Magnesium is right below calcium on the periodic table"
Other way around. Strontium is below calcium.
Another common mineral everyone should know - natural ice. Sorry, the ice in your freezer does not count - it's man made. But glacial ice, pond ice or even snow fits the definition of a mineral. (A naturally occurring, homogeneous inorganic solid substance having a definite chemical composition and characteristic crystalline structure, color, and hardness)
Um, seashells are made of aragonite, but that's OK, calcite is a good enough answer.
Andrew, nice job throwing out the only word you remember from intro geology, but youre still an idiot. Troll elsewhere.