The theme for National Chemistry Week (NCW) this year is Chemistry Rocks!1 During NCW, which this year will be held October 22 – 28, many chemical educators will be focusing on the chemistry of rocks and minerals. To prepare for NCW, I’ve been in the lab conducting tests on the chemical and physical properties of various geological samples. In my investigations I’ve found that hematite is a particular mineral that is easy to acquire and quite amenable to experimentation.
The chemical name for hematite is iron (III) oxide, and its formula is Fe2O3.2 Hematite is the main constituent in iron ore,3 from which iron is extracted to make steel.4 The color of hematite varies depending upon the sizes of its constituent particles. Powdered or fine-grained hematite is red or reddish-brown,5 while larger stones may are steel-grey or black. In fact, fine-grained hematite on the surface of Mars is responsible the characteristic color of the red planet.5,6
Hematite can be easily purchased quite inexpensively in the form of decorative beads at craft stores such as Michael’s or Jo-Ann Fabrics. I recently purchased some beads labeled “magnetic hematite” (MH), and “hematite luster cube stone” (HS). I ran some various tests on these beads to see if they did indeed contain hematite.
Figure 1: Beads sold as “hematite luster cube stone” (HS, left), and “magnetic hematite” (MH, right).
I decided to start by testing the density of each bead type. Sure enough, the densities determined for both MH (5.0 ± 0.5 g cm-3) and HS (5.2 ± 0.4 g cm-3) agreed with the density of hematite (5.26 g cm-3)6 to within experimental error. However, I observed quite different magnetic properties for MH than for HS; the former displayed much stronger room temperature magnetism than the latter. Given that hematite is weakly ferromagnetic at room temperature,7 I decided to run some more tests to see if I could observe differences between the two types of beads. In the video below, you can view my investigations:
Thus, as far as I can tell, the beads sold as MH do not actually contain hematite. Rather, I think these beads are more similar to ceramic magnets such as strontium ferrite.8 While I’m not entirely certain that the HS beads contain hematite, they do seem to show some of the predicted properties of this mineral. Therefore, I do think the HS beads do contain some hematite.
I saw several types of beads, other than the ones reported here, sold at Michael’s and JoAnn fabrics that purportedly contain hematite. I’d enjoy hearing about it if you conduct some tests on other “hematite” beads. Also, if you decide to try out some of the experiments reported here during NCW (or any other time), be sure to let me know how things worked out for you. I’d love to hear if you have any interesting observations that I missed. I would also like to know if you have any suggestions for further experiments with these “hematite” beads. I look forward to hearing from you. Happy experimenting!
- Interestingly enough, the theme for NCW in 2018 is “Chemistry is Out of this World!”: The chemistry of and in outer space. Therefore, the experiments reported herein would also be a good fit for NCW 2018.
Please refer to the ACS Guidelines for Chemical Laboratory Safety in Secondary Schools (2016). Some additional information on these guidelines can be found in a Pick at ChemEd X.
RAMP: Recognize hazards; Assess the risks of hazards; Minimize the risks of hazards; Prepare for emergencies
Planning and carrying out investigations in 9-12 builds on K-8 experiences and progresses to include investigations that provide evidence for and test conceptual, mathematical, physical, and empirical models.
Planning and carrying out investigations in 9-12 builds on K-8 experiences and progresses to include investigations that provide evidence for and test conceptual, mathematical, physical, and empirical models. Plan and conduct an investigation individually and collaboratively to produce data to serve as the basis for evidence, and in the design: decide on types, how much, and accuracy of data needed to produce reliable measurements and consider limitations on the precision of the data (e.g., number of trials, cost, risk, time), and refine the design accordingly.