Bathroom Geology

Do you ever see pictures of beautiful geology all over the world and think “WOW, I don’t think I’ll ever be able to see that in person”? Well, think again. This post is dedicated to helping you find amazing geological finds in a place I can guarantee you will visit just about every day: the bathroom (and no, I’m not just talking about coprolites)!

The goal of this post is to teach you a little about the types of rocks you might see the next time you’re in a restaurant bathroom, a bathroom at the beach, the library bathroom, or even the bathroom in your own house! You might be thinking “oh, but what can I learn from a bathroom?!” Well, you just might be surprised. So, let’s get to learning!

Figure 1. A granite countertop from a restaurant in Richmond, Virginia. This granite is unique because of the concentric zoning of the crystals- this means that the crystals were cooling at slightly different temperatures, giving it the unusual appearance of the larger crystals (where my finger is pointing). Different elements are crystallizing out of the magma at different temperatures, which gives it this look of almost like tree rings.

Our first stop is a small restaurant in Richmond, Virginia. The food was good, but the real treat was finding the granite countertops inside the bathroom (Figure 1)! Take a look! Granite is an intrusive igneous rock: meaning, the magma from which the rock was made cooled slowly underground. We know this because of the very large crystals that we can see! Crystals grow from the liquid magma; the longer they take to cool, the larger they grow. Now, let’s look more closely at these big crystals. If you look at the large, light pink colored crystals where my finger is pointing you might see that they are what we call “zoned”- meaning, there are alternating circles of slightly different colors inside the crystals- their rounded shape means we’d assign the term “concentric zoning” to them. This actually tells us something really cool about their cooling temperature!

Figure 2. Bowen’s Reaction Series explains the pattern of what minerals and elements cool at what temperatures. As magma cools, certain materials are always crystallized first and pulled out of the pool of magma. Photo credit: National Parks Service

Magma cools at different rates- depending on where it is on Earth or the types of materials from which the magma is made. This rate of cooling determines how and when certain minerals form, or crystallize. In other words, geologists know quite well at what temperature a mineral will form within a magma chamber as it cools down. This predictable pattern of mineral formation with cooling temperatures is called Bowen’s Reaction Series (Figure 2). When this happens, it means the chemistry of the still-liquid magma changes quite a bit!
To put this into a more delicious and more relatable example, think about a giant jar of Starburst-with red, pink, yellow, and orange evenly mixed in. Let’s say you give this jar to me (I really love Starburst). I will preferentially eat all of the orange ones out of it; then the pink; then the red; and finally, we’ll only be left with yellow (gross, who eats the yellow ones?!). We’ve changed the overall composition of the magma (i.e., the jar of Starburst) by preferentially pulling out one type of material in a specific pattern. Now, take a look at the giant crystal my finger is pointing to- the zoning is going back and forth between a sodium and a calcium rich solution in the feldspar (the name of the mineral)-this indicates that the temperature of the magma where this was cooling was changing slightly, alternating between a little hotter and a little cooler.

Figure 3. This granite has almandine garnet as an accessory mineral, which means that the magma from which it formed had a lot of aluminum in it!

Now granite is really cool and it’s a very common bathroom countertop, so let’s look at another example (Figure 3)! This granite was part of a larger piece of rock that was installed in a private home bathroom in Fayetteville, North Carolina. This little piece was leftover, so the countertop store let me have it! This granite is similar to the granite from above, but it doesn’t have any zoning, meaning it all cooled without any weird changes in temperature. However, it does have one pretty cool feature-the garnets! These garnets (the little red crystals) are of the almandine variety. Almandine is a type of garnet that has a lot of iron and aluminum in it. Garnet forms in granite as an accessory mineral (meaning, not a major component) and different garnets can mean different things. In this particular sample, this almandine garnet means the magma was aluminous; meaning, there was a lot of aluminum in this magma!

Figure 4. This migmatite formed from the combination of an igneous and a metamorphic rock; this rock also has ptygmatic folding, which is seen in the lighter layers as the squiggles running across the rock. These form from high temperature and pressure and from one of the rocks being much more viscous than the other (in this case, the lighter rock is much more viscous than the darker rock- much like honey is more viscous than water).

I found this gem at a women’s bathroom in the San Francisco airport (SFX) last year (Figure 4)! This rock is called a migmatite. A migmatite is unique in that it is a cross between an igneous (formed directly from cooled magma or lava) and a metamorphic rock (a rock that was exposed to heat and pressure after its original formation). The dark and the light material you see here are from two totally different processes. The light material here is mostly quartz (the same mineral that we call amethyst or rose quartz–quartz occurs in a variety of colors). The lighter material is much more viscous-meaning, it resists flowing (like honey or molasses), while the darker stuff (primarily from minerals called pyroxene or hornblende) has a lower viscosity and flows more easily. Now, do you see how the light colored material exhibits small and irregular folds? These folds are what geologists call “ptygmatic”. These ptygmatic folds generally occur at pretty high temperatures and pressure; these variables cause the layers to fold and buckle the way that they do because of the differences in viscosity. The high temperature and pressure, along with the high viscosity of the light material, will cause these types of folds to form (these are also known as “passive folds”).

Figure 5. Internal and external molds of fossils at the St. Petersburg beach bathroom! These form when the actual shell of a creature is worn away and all that is left is the mud that either filled the inside of the shell or the mud that formed around the shell.

I recently saw this one (Figure 5) at the St. Petersburg beach in Florida, pretty close to where I live. These blocks are part of the public bathroom walls and as you can see, these bathroom walls are chock full of fossils! Wow! These fossils are from Florida and they’re pretty recent–no more than 10-20 million years old. They’re also primarily mollusks, the large group that contains octopuses, clams, snails, and oysters. Imaged here are snail fossils-you can identify these snails by their long, delicate shells- and clam fossils-you can identify those by the much larger shells that have ridges along the edges. These types of fossils are called “molds”-this means that the shell itself has been worn away and all that’s left is the sediment that either filled in the shell or the sediment that formed around the shell. The internal molds are where you can see an actual 3D shape of the inside of the shell, whereas the external molds are where you only see an impression of the shell.

Figure 6. Labrodorite is a type of feldspar that has an easy to recognize iridescent sheen. Labrodorite is most commonly found in mafic igneous rocks, like basalt!

Last but not least, my mom snapped this picture of her bathroom just for this post (thanks, Mom!)! Labradorite is a beautiful mineral-it’s a type of feldspar, which is in the same group as the lovely pink minerals seen in the granite in Figure 1. What makes labradorite so different, though, is that this feldspar doesn’t form in granite-it forms in a very different type of rock, like basalt! Basalt is an extrusive igneous rocks, so it forms from lava that cools at the Earth’s surface. Basalt is found in places like Hawaii, where it comes out of volcanoes, or at mid-ocean ridges, where new seafloor is being made. Basalt is mafic, meaning that it is full of heavy minerals like iron and magnesium. Labradorite is famous for its iridescent sheen-you can see it here in Figure 6!

I hope that this post has shown you that you don’t need to travel to fancy and far away locations to see real and beautiful geology up close. Sometimes, interesting geology can be as close as the nearest bathroom! Next time you see one of these counters, stop and take a look! What do you see? Do you see fossils? Garnets? Zoning? Do you see something entirely different? Before I go, I’d like to thank geologists Cameron Hughes, Zachary Atlas, Elisabeth Gallant, and Jeffery Ryan for help with identifying some of the details in these rock samples!

Advertisements

One thought on “Bathroom Geology

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.