Selenite crystals are only a 2 on the Mohs scale

The final installment of my mineral posts has taken awhile to get here, and it took me a fair bit of digging (no pun intended!) to find more information about the featured rocks. Whatever I did find initially seemed to come from either Wikipedia — quoting scientific sources that I struggled to understand — or alternative health websites focused on the healing powers of crystals. For example, I learned from health-line.com that selenite crystals (above) are a form of gypsum, formed when sulfate and calcium-rich saltwater evaporate. However, I didn’t give up, and eventually I was successful in researching my other samples.

Rhodochrosite is a manganese carbonate mineral; it comes in a range of colors but the name refers to its tendency toward red. Why this specimen seems to be green I can’t really say! Regarding the blue Smithsonite in the background, it was named in honor of the man who first identified it (in 1802), James Smithson — the same man who helped establish the Smithsonian Institute in Washington, D.C.

Before visiting the Angels Camp Museum, I had no idea that copper may actually be found in its pure state, as native copper, rather than as an ore, mixed with other rock. I was already somewhat familiar with sulfur, if only for its unmistakeable bright yellow color and its infamous “rotten egg” smell. Sulfur has also been called brimstone, which comes from the Middle English for “burning stone.” Unsurprisingly, one place to find sulfur forming is near volcanic vents and fumaroles — and as unpleasant as it may smell, it’s an essential element in all living things.

I was initially stumped on searching for “calcupyril,” seen in the above photo. Then I decided that maybe what I was looking for was chalcopyrite, which is an important copper ore that’s often confused for gold. Since I barely managed to fit it into the picture and admittedly didn’t pay much attention to it at the time, I unfortunately can’t really do it justice here — which does seem a bit unfair since chalcopyrite has been been in use for over 5,000 years!

Finally, this colorful sample of Zebra sandstone sitting in the display case seriously caught my eye — but I’ve had trouble pinning down any information about it. The best I could manage was a Pinterest page showing a very similar looking piece with a quote from the Illinois State Museum: “The bands in this Zebra sandstone come from red iron oxides and white to yellow quartz sandstone.” Sandstone is a sedimentary rock that usually comes in muted colors, so it’s fascinating to consider the process that went into forming a sample this flashy!