Chemistry ROCKS!

macroscopic view of table salt

I must admit, I feel somewhat of an imposter in the chemistry world as I have a Master’s degree in geology. While my research was in the field of geochemistry, I (like most geologists) have a deep and abiding love for rocks and minerals. If you walk in my classroom, you will find various rock samples on my desk, a poster of minerals from around the world and of course, boxes full of rocks! I have only taught a geology class once, so I have needed an outlet for all this pent up love for rocks. The great thing about geology is, it's all about chemistry! I want to share one of my favorite links between geology and chemistry that my students think is pretty cool too.

If you use Modeling Instruction, you might be familiar with the “Crystal Structures” activity using Mercury software. I wrote about my switch from Mercury to MolView on my blog a few years back and Michelle Okroy wrote about the program in her blog post, MolView: An App to View Structural Formulas and Models, as well. This activity allows students to see how different types of compounds vary at the particulate level. I like to extend this activity to show students how microscopic observations impact macroscopic observations. You can show these structures to students as part of a whole class discussion or have your students open MolView and manipulate the structures themselves. Alternatively, you might consider using the Tools tab in MolView to copy the embed code of specific structures and insert them into your own website so students don't need to figure out how to use the website. You can see samples of the interactive structures that can be embedded below (Figures 1B and 2B).

The first example I show is graphite and diamond (see Figure 1).


Figure 1A: Particle view of graphite (left) and diamond (right)

Figure 1B - Interactive 3D particle view of graphite



Graphite works great in pencils because it breaks off in sheets as you write. Diamond is made of the same atoms, but a completely different structure gives it completely different properties. 

The next example is sodium chloride (table salt), also known in the geology world as halite (see Figure 2).

Figure 2A:Particle view of sodium chloride

Figure 2B: Interactive 3D particle view of sodium chloride


Students quickly see that halite has a cubic crystal structure. With a magnifying glass and some table salt, students can see how the microscopic structure extends to the macroscopic structure (see Figure 3).

Figure 3: Macroscopic view of table salt


You may already show your students the first examples I have shared. I hope this last one, calcium carbonate, is new to you! It is known in the geology world as calcite (see Figure 4).

Figure 4: Particulate view of calcium carbonate


Students usually describe the shape of calcite as a slanted rectangle. The geology term is for that shape is rhombic. This is when I get out my sample of optical calcite and use my iPevo camera to show how the rhombic structure of calcite produces double refraction of light that passes through it (see Figure 5).


Figure 5: Sample of optical calcite that shows double refraction of light


Students really love seeing the double refraction. What students love even more is when I nonchalantly pull a rock hammer out of my desk and smash a piece of calcite (not my optical sample!) so they can see that not only does calcite grow as a rhomb, it breaks in rhombs as well (see Figure 6). Students are always surprised to learn that the optical calcite was not cut to be that shape.

Figure 6: Calcite broken into bits still shows rhombic shape

Most students will never take a geology course so I like to throw in some Earth Science tidbits wherever I can. Calcite makes a reappearance in my acids and bases unit because the field test for determining if a rock contains the mineral calcite is dropping dilute hydrochloric acid on it to see if it fizzes! 

If you are looking for a new way to show your students that chemistry rocks, hopefully geology can give you hand! If you are logged into ChemEd X, you can find directions to help you get started using MolView in the Supporting Information.


Students who demonstrate understanding can plan and conduct an investigation to gather evidence to compare the structure of substances at the bulk scale to infer the strength of electrical forces between particles.

*More information about all DCI for HS-PS1 can be found at and further resources at


Students who demonstrate understanding can plan and conduct an investigation to gather evidence to compare the structure of substances at the bulk scale to infer the strength of electrical forces between particles. 

Assessment Boundary:

Assessment does not include Raoult’s law calculations of vapor pressure.


Emphasis is on understanding the strengths of forces between particles, not on naming specific intermolecular forces (such as dipole-dipole). Examples of particles could include ions, atoms, molecules, and networked materials (such as graphite). Examples of bulk properties of substances could include the melting point and boiling point, vapor pressure, and surface tension.

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Comments 2

Jeremy Wanak | Tue, 05/28/2019 - 22:00

Lauren, I found your post in response an interest in teaching physical and chemical properties from a rocks and minerals perspective.  I've considered the simple properties of rocks tests (scratch test etc.) to have students think about properties.  Do you have any suggestions in good and simple rock/mineral tests that would be helpful with freshman physical science?

Lauren Stewart's picture
Lauren Stewart | Fri, 06/14/2019 - 18:57

Hi Jeremy,

I also teach freshmen physical science so I love this idea! As a geologist, the first thing I would look at is color though honestly, that usually does not tell you much unless it's bright yellow sulfur. Next step would be an acid test, then scratch test and streak test, then I would look for cleavage/fracture. 

Geologists frequently use dilute HCl (~1M) to test for the presence of carbonates. Carbonate will fizz when a drop of acid is added to them. Calcite is a great example. Additionally, you can determine if a mineral is calcite (Ca(CO3)2) or dolomite (CaMg(CO3)2) based on how much it reacts with the acid. 

Streak test is also a fun one. If you can get a sample of specular hematite, it is grey and sparkly in color but it streaks red because it is an iron oxide. If you want to do scratch test, talc or gypsum and quartz are easy to get and show two ends of the spectrum. You can scratch talc and gypsum with your fingernail and quartz will scratch glass. 

Halite and calcite as mentioned above are both great examples of cleavage. Crystal habit can also be a useful property. If you can get a nice crystal of quartz, it will be hexagonal. If that quartz has a broken edge, you will see it doesn't break that way buy instead has conchoidal fracture do to its amorphous structure. 

Some minerals additionally have special properties like magnetite is magnetic. 

Having students use a dichotomous key to classify a few minerals would be a really cool exercise for freshmen physical science, especially if you picked a few that have similar colors like calcite, quartz and gypsum. Students would have to use a variety of properties to identify them.

Hope that helps! I am definitely going to add this to my lesson plans for next year!