A slight cringe at a Yellowstone National Park sign

I've been back from my month long trip to South Dakota & surrounding areas for a couple of weeks now.  There's lots of great geology to talk about, so a lot more will come as I get around to it.  But for now, just a post about a sign at Yellowstone that reads:

"Deep within the Earth, heated water dissolves and then transports silica, the same mineral found in sand and glass, to the surface.  During geyser eruptions, silica is deposited around narrow 'vents' or openings.  Over time this mineral, called geyserite or sinter, forms mounds of varying sizes and shapes."

The sign that's wrong about minerals.

EEeeeeeessssshh!!  If you zoom in on that photo above, you might be able to make out the text under the central picture of Castle geyser.  As to the science on the sign, the basic idea that hydrothermal fluids dissolve & reprecipitate silica is fine, and this sign probably communicates correct information to the reader for the most part.  However, it perpetuates a misconception in the understanding of what a mineral is.  "Silica", "geyserite", and "sinter" are NOT minerals.  At least, not in the geologic sense, and since this sign is communicated geoscience information, it ought to use geologic terms correctly.  

Silica is a chemical compound, with the formula SiO₂.  All minerals are chemical compounds, but chemical compounds are not necessarily minerals.  For one thing, minerals have to be solid.  So if silica is dissolved in water, it's not a solid, it's now a component of a liquid.  Using the term "mineral" in this fashion is a bit like the way the term is often used in nutrition, where various elements like calcium & iron are often referred to as "minerals".  They are sometimes referred to as "mineral nutrients" or "dietary minerals", but neither of these terms are very satisfying either.  I'm not sure why the term mineral ever got used in this fashion, since none of the "minerals" referred to in nutrition are minerals, they are simply elements.  But again, this sign is attempting to communicate geoscience, and in geoscience if something is dissolved in a liquid, it is most definitely not a mineral.  


Now suppose our silica is in a solid form, does that make it a mineral?  Not necessarily.  Several minerals are made of silica (quartz & its many polymorphs), but silica itself is not a mineral, it is a chemical compound.  The reason silica is not a mineral is because minerals are defined not only by their chemical composition but also by their atomic structure.  Quartz & all those other silica polymorphs each have a distinct atomic structure.  Silica can also form solid materials that are not minerals, such as opal.  Opal is a solid that does not have a crystalline atomic structure.  Glass is another solid material that also does not have a crystalline atomic structure.  A crystalline atomic structure means that the atoms are all lined up and bonded together in an orderly fashion that repeats itself in three dimensions thousands and millions and billions of times, depending on the size of the grain.  Non-crystalline solids are solids where the atoms are a bit more jumbled up & irregular.  So minerals are defined by their chemical composition AND their atomic structure.  Silica is a more general term that only means chemical composition, but doesn't specify the atomic structure.  


Geyserite is also not a mineral.  "Geyserite" is something of a generic term referring to the solid silica that is deposited around geysers.  So this is at least solid, but it still isn't a mineral.  Most of geyserite is the material known as opal, and as I already explained above, opal is not a mineral because it does not have a crystalline structure at the atomic level.  


Sinter is another term that really refers to the porous nature of the geyserite, so this is a term that's really about the physical attribute of the aggregation of the various grains of opal.  So really, this is a rock term.  


So what is a mineral?  That I'll save for another post.  


But why write this post?  Who cares?  I teach a course in minerals to undergraduate geology majors.  One of the most important concepts of the course is "what is a mineral?" and what is not.  Definitions, especially in science, are extremely important.  A geologist's understanding of the term "mineral" can't be gray & fuzzy; it needs to be precise & accurate.  Many geology majors grow up with an interest in natural phenomena & are likely to see signs like this one at Yellowstone, and they get these confused definitions in their heads.  In education, misconceptions (things we think we know but are actually wrong) are really, really hard to get out & get corrected.  


On the first day of my mineralogy class, I ask my students to simply list the name of every mineral they can think of.  When they took their introductory geology course, they learned about 20 or so minerals, so this exercise is intended to require them to recall that information.  But the answers given often include things that are not minerals.  Answers like "quartz, feldspar, granite, calcium" sometimes show up.  The first two are fine minerals, but #3 is a rock and #4 is an element and neither of them are minerals.  This shows that the students don't have a clear & precise grasp of what a mineral even is or is not.  In my experience, this is pretty typical for students at this stage of learning; hopefully at the end of the course they've got the concept mastered!  

But beyond the students in a mineralogy course, confusion about science abounds in our society.  A basic knowledge of the differences between minerals, elements, & chemical compounds is junior high level science.  So I cringe when these differences are misrepresented on a sign in a national park that's intended to communicate scientific information to the public.  The problem basically boils down to this: there's a precise, careful definition of the term that's used by those who know, and there's the loose, flimsy definition of the term that's used more in the general public.  A sign communicating geoscience to the public I think ought to be a bit better.

Geology with First Graders

Last week, based on an invite from the teacher, I paid a visit to my oldest daughter's first grade class to talk about geology.  I knew they had been learning about sand, so my job was to take it up to 11.  I also knew, based on what my daughter brings home, that they had previously talked about solids, liquids, & gases, but otherwise they don't get a whole lot of science in first grade.

I brought with me some samples; the ONU Geology program has lots of samples of rocks & sands (obviously), so I took some especially relevant ones to show the kids.

The main point I tried to get across to them is this: different kinds of sand come from different kinds of rocks.  I figured for first graders that wasn't a bad place to start.  The idea is to have them connect in their minds that rocks, when eroded, will form sand, and that there is a direct connection between these two kinds of materials. This is, really, their first introduction to the rock cycle.

I took with me 4 samples of sand.  The first one is a typical quartz sand in a jar that had a couple of nice shells in it.  That one I passed around first and had each student rotate the jar of sand until they found the secret prize inside.  Lots of wide eyes and careful looking at this point!









After I had their interest, I then showed them three other sands and three related rocks.  The white sand here is loaded with calcareous material, and the white "rocks" are pieces of some kind of coral from the same beach.

The green sand is olivine rich, with black chunks of basalt and white pieces of crushed coral.   The green rock is dunite.

The black sand is eroded basalt cinder for the most part, and the black rocks is a basalt with obvious pahoehoe texture on the top surface.












I talked about the three different rocks as representing the three major rock types: the dunite as a metamorphic rock, the basalt as igneous, & the corals as sedimentary.  They didn't quite pick up on the differences or the words well (and I didn't expect them to), but they were at least exposed to the terms.  They liked the basalt the best - it is a pahoehoe sample from Hawaii, so we talked about lava & how it is a hot, liquid rock that cooled to form this solid material.  They were really impressed with that!

Granted the olivine rich sand didn't come from the erosion of dunite, but the samples allowed them to see that there are connections between rocks and sediments.

After we looked at those, we ended with this question: what might happen if you took a sand, and squeezed it really really really hard?  You can't do this with your hands, but the Earth is able to squeeze sands hard enough that they turn back into rocks!  At this point I pulled out a couple of sandstones that are easily seen as grains of sand that are all stuck together.  Minds blown!  That was another moment where their eye-brows were all raised.  Again, here they were exposed to another idea from the bigger concept of the rock cycle.

It was a really fun experience.  These students are considerably younger than the ones I'm used to teaching!  And, if I'm totally honest, they are in general a lot more enthusiastic about learning than some college students!  :-)

A Growing Collection of Geology Field Photos

Today over at Georneys, Evelyn suggested, in what's sure to become a geoblogmeme, posting geology pictures.  I love it when geologists share their photographs, and since late August I've started building my collection of geology photos and posting them on Google+.  It all got started when I decided to take a leap and submit one of my photos to the NASA site Earth Science Picture of the Day, and they accepted it.  I mainly did that because I was a bit bored of all the cloud formations that tend to dominate the EPoDs (need more geologists submitting their pics to this site!).  Anyway, that experience as well as the huge amount of great photo sharing on G+ led me down this path.

Isoclinal folds in high-grade gneiss, eastern Blue Ridge, Southern Appalachians.

The pics are being collected in an PicasaWeb album.  When I post them on G+, I give a longer description & explanation so my followers can learn something cool about geoscience.  All of the photos are geotagged and their locations can be seen on the map in the PicasaWeb album (unfortunately, the same album viewed in G+ does not have the spiffy googlemaps with it), so that others can visit these locations and see for themselves.

Chilled margin in granite, St. Francois Mtns., MO

I've cross-posted the links to the G+ posts on my BookFace & Twitter accounts, but so far the blog here hasn't seen them.  I've also tagged each of these posts with the hashtag #geopic.  In this way, anyone can see the photos and search for the descriptions I wrote about them easily on G+.  I'm happy to let any geoscience instructors use them (unaltered, of course) as examples in their lecture slides.  A lot of photographers post beautiful pictures of landscapes, and I'm not a serious photographer in that way; these are meant for science, not necessarily for art.

Deformed mudcracks, Valley & Ridge Province, east TN.

So without further ado, here's the link to the collection:

https://picasaweb.google.com/106934864033790932269/GeologyFieldPhotos

The collection so far includes 14 pictures (I post about 1 per week).  I also upload the photos to my panoramio account so they can be viewed in Google Earth & Maps.  The collection so far includes about 10 structures (3 folds, a textbook delta clast, deformed mudcracks, en echelon veins, liesegang rings, a chilled margin in granite, and GIANT-size joints & cross beds), 2 landforms, 1 fossil, and 1 mineral/crystal.  I guess that's a bit skewed toward the structures!

Delta clast in gneiss, Parry Sound Shear Zone, Ontario, CA.