You’ll almost never see gorgeous red realgar crystals on display, and if you do, it won’t be for long. Why? It turns out that realgar is one of several minerals that changes and degrades when exposed to light.
Realgar from Shimen, Changde Prefecture, Hunan, China
If left on display, this light-sensitive crystal would begin to turn dark and eventually change into an entirely different mineral: the powdery orange pararealgar, shown below. This happens because of the energy carried in certain wavelengths of light. When that energy hits atoms in the crystal, it causes some of their atomic bonds to break and rearrange into a different structure. For this reason, realgar is one mineral that will always stay inside the box!
Pararealgar from Royal Reward Mine, King County, Washington, USA
Even common minerals like amethyst and fluorite can begin to fade over time, especially if exposed to bright sunlight for long periods. We recommend displaying your treasures on a shelf rather than a windowsill.
What do you think the object on the left has in common with the three objects on the right? This question isn’t too hard to answer: they’re all fossilized clams. But why do they look so different?
The clam on the left is the mineralized shell of a clam from Coal Creek, Washington. After the clam died, its shell was encased in sedimentary rock; while that rock was forming, foreign minerals grew and replaced the original calcium carbonate the shell was created from when the clam was alive. (These replacement minerals are responsible for the dark color.)
The clams on the right, on the other hand, are agate molds of clam shell insides. They come from Green Creek in Washington. Their tops have been polished a bit to give them a nice shine, but the shapes are natural. After these clams died, agate filled in the insides of their shells, and the shells themselves dissolved away.
These fossil clams show just two of the many different modes of fossil preservation!
These concentric green circles look like some kind of painting or an old-fashioned LP gone wrong, but in reality this mesmerizing pattern was created by nature. This is the mineral malachite, a copper carbonate associated with ore deposits.
Malachite forms when other copper minerals like chalcopyrite react with acidic water percolating through the rock. This water can carry copper atoms along for a bit before the copper begins to combine with other atoms and grow minerals like malachite. Sometimes, the water drips into open cavities in the surrounding rock, and malachite will grow as a stalactite or stalagmite the same way other cave formations do.
The photo above shows a slice through a malachite stalactite. The concentric rings come from the growth of the stalactite in fits and starts, and the light and dark colors reflect small changes in the water chemistry over time.
Even though it was made by nature, a little human ingenuity helps this pattern to shine: the rings are most striking in malachite pieces that have been cut and polished like this one.
One of the most famous lapidary materials to have ever come from Oregon, Biggs Picture Jasper has captivated many with its beautiful blue and brown lines and swirls. This slab’s pattern is characteristic of the early material found near the town of Biggs Junction.
Biggs Jasper was discovered by modern rockhounds in 1964 after a massive flood tore through the canyons just south of the intersection between US-97 and present-day I-84. The excitement over the find was so great that road repairs in one canyon were briefly delayed while rock enthusiasts removed boulders of the material, according to rockhound Dale Rhode. Biggs Jasper stands out best when cut and polished as cabochons or slabs.
Jaspers are a grainy variety of chalcedony (silicon dioxide) rendered opaque by incorporation of other minerals and foreign material. Brown, red, yellow, and white colors are most common; the blue of Biggs Jasper stands out.
The most famous precious opal in the US comes from Virgin Valley in Humboldt County, Nevada. Petrified tree trunks buried in volcanic tuffs have developed opals with gorgeous play of color.
In this specimen, white common opal infills large holes, while blue and green precious opal is found in pores preserving the tree trunk’s original grain structure. This specimen is from Richard and Helen Rice’s original family collection.
Have you ever collected opal from Virgin Valley? Where are some of your favorite opal localities?
Join us for a new, online feature and discover “What’s In The Box?” with curator Leslie Moclock. Leslie will take you behind the scenes to see some of the beautiful and interesting specimens currently off display. Follow us on Facebook, Twitter, Google+, or Instagram to see photos and learn a little about each one as we dig deeper into our rock and mineral inventory.
We are in the midst of a massive Collections inventory project that, when completed, will allow us to start rotating some of these back room beauties into the galleries for display. “What’s in the Box?” gives YOU a sneak peek here first! Discover our hidden treasures as Leslie makes her way through Collections storage. Curious to know more about a particular object? Simply reply to the original post on your social media platform of choice with your questions. And don’t forget to share these finds with your friends!
Check out #RiceWITB and find out “What’s In The Box?” along with Leslie as she uncovers these treasures and shares them with you! If you want to see even more photos of collections items, don’t forget to join us on Facebook for Mystery Mineral Mondays, too.