This event has ended. Keep an eye on our website and social media for more fun events!
minerals
How Do Geodes Get Their Colors?
Geodes are stones with a secret–at first glance, they seem like nothing more than the grey rocks you might see on walk around your neighborhood. Then–crack!–once they’re broken open, they reveal their inner beauty: a tiny cave filled with some of the world’s most spectacular, colorful crystals.
Born out of lava
Geodes are formed when there are pockets of air within rocks. This often happens after volcanic eruptions when lava cools around air bubbles. These pockets leave space for groundwater to seep in. But the water itself doesn’t produce geodes–it brings along minerals which stay in the rock even after the water evaporates. The minerals then start to build on each other to form crystals. It can take thousands or even millions of years for these crystals to form. The larger the crystals are, the older the geode is.
So what gives them their color?
The same minerals that form crystals can give them their glorious colors. Additional elements can also make their way into the mix and provide their own unique shades. Iron will give crystals a red or purple color, titanium will create blue, nickel or chromium leads to green, and manganese produces pink crystals.
While geodes can be naturally colorful some are artificially dyed. These dyed stones often have a brighter, more intense color than what appears naturally. Why do people dye geodes? Colorful geodes tend to sell well and can be a cheap way to imitate rare stones.
Come to the museum and check out the geodes of various colors on display in Hillman Hall of Minerals and Gems.
Explore nature together. Visit Nature 360 for more activities and information.
A Perfect Mineral for the Christmas Season
by Debra Wilson
How can you decorate a mineral for Christmas? If it’s the right mineral, all you need to do is shine a SWUV (short wave ultraviolet) light on it. Such is the case with a mineral that is known as “Christmas Ore.” Under normal light it looks like kind of a drab rock as the one in this photo does.
This specimen of calcite (tan color), willemite (brown color) and franklinite (black color) is on display in Hillman Hall of Minerals and Gems in the Fluorescence & Phosphorescence exhibit and was donated by the Sterling Hill Mining Museum for this exhibit. It originated from the Sterling Hill mine in Ogdensburg, in the Franklin Mining District of New Jersey. When you shine the SWUV light on it you will see why it is called “Christmas Ore” because it glows with the colors of Christmas. The calcite glows a bright red and the willemite glows a bright green, as you can see in this photo.
This glowing is known as fluorescence and the Franklin Mining District is known as the fluorescent capital of the world. The Franklin and Sterling Hill ore bodies are the source of at least 350 mineral species.At present, over 80 fluorescent mineral species are known from the area. Willemite and calcite are the most common fluorescents in these ore bodies and are known as “Christmas Ore” when they occur together in the same specimen.
So, what causes the fluorescence? Fluorescence usually occurs when specific impurities known as “activators” are present within the mineral. These activators are typically cat ions of metals such as: tungsten, molybdenum, lead, boron, titanium, manganese, uranium and chromium. Rare earth elements such as europium, terbium, dysprosium, and yttrium are also known to contribute to the fluorescence phenomenon. Fluorescence can also be caused by crystal structural defects or organic impurities. Calcite (CaCO3) and willemite (Zn2SiO4) are examples of minerals that in their pure state do not fluoresce but add a little divalent manganese (Mn2+) and they will fluoresce red and green, respectively.
There are two other specimens of calcite and willemite, also from the Franklin District, in the Fluorescence & Phosphorescence exhibit, shown here under normal light and under SWUV light.
Come to Hillman Hall of Minerals and Gems to hear a more detailed explanation of the phenomenon of fluorescence and see all 21 specimens in the exhibit from world-wide localities that glow under the ultraviolet lights.
Debra Wilson is the Collection Manager for the Section of Minerals at Carnegie Museum of Natural History. Museum employees are encouraged to blog about their unique experiences and knowledge gained from working at the museum.
Related Content
Thanksgiving and Nutritional Mineralogy
Ask a Scientist: Why do some minerals glow?
Carnegie Museum of Natural History Blog Citation Information
Blog author: Wilson, DebraPublication date: December 13, 2018
Share this post!
BBQ Chips
How about some BBQ chips with your burger?
Just kidding! BBQ chips is the nickname for this wulfenite with mimetite specimen on display in the Masterpiece Gallery.
Manhattan Project Glass
By Debra Wilson
The Section of Minerals collection contains many specimens with interesting stories of historical significance. One such story is about an unusual faceted stone.
As part of the Manhattan Project, the mission of the Hanford Site in Benton County, Washington was to produce plutonium for the atomic bomb. This included the first bomb tested at Trinity Site in New Mexico and the Fatman bomb that was dropped on Nagasaki to end World War II in 1945. The viewing windows that the scientists looked through in the chemical processing buildings (AKA plutonium recovery buildings, where the plutonium was being extracted from the fuel rods) were made of 70% lead to protect them from the highly radioactive material they were working with.
When the buildings began being salvaged in 1990, five of these radiation windows were sent to a salvage yard in Walla Walla, Washington, where they were stored in a warehouse. Sometime during the two decades of storage one of the panes shattered. When the broken pieces were sold, Patrick Kelley of PAK Designs in North Carolina was able to acquire two pieces. He faceted the Rectangular Baguette Cut, 51.4 carat gemstone in 2013 that now resides in the Section of Minerals collection. Note the yellow color of the glass due to the high lead content.
This stone is now on display in the Treated & Synthetic Stones case in Wertz Gallery.
Debra Wilson is the Collection Manager for the Section of Minerals at Carnegie Museum of Natural History. Museum employees are encouraged to blog about their unique experiences and knowledge gained from working at the museum.
Related Content
What Does Pittsburgh Have in Common With Mount Vesuvius?
Carnegie Museum of Natural History Blog Citation Information
Blog author: Wilson, DebraPublication date: August 1, 2018
Share this post!
Wire Silver
You might not recognize these at first glance, but these new specimens in Hillman Hall are a common metal: silver. Wire silver from China to be exact. It is hard to imagine pieces like these are the same material as delicate jewelry, isn’t it? Get a close look at these specimens in the Native Elements case in the Systematic Collection.
Photo by Debra Wilson, Collection Manager, Section of Minerals