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10/05/2026

Most minerals are not things to be eaten. Some minerals are even toxic if digested. So it may be a surprise to learn that there is a mineral that you eat every day! Halite is an evaporite mineral with chemical formula NaCl, also known by the much more common name of table salt.

Being an evaporite mineral, halite forms as a residual product when bodies of water evaporate and leave it behind. Water can contain dissolved salt, but when it turns into gaseous form, it can no longer trap the Na+ and Cl- ions in solution, and so they deposit, combined into NaCl. This happens commonly in bodies like the ocean, hence the name “sea salt”.

Halite, when forming in large quantities, can form in a massive form, such as that seen in salt flats, or in formations known as “hopper crystals”, where crystals form in layered ziggurat shapes.

To see this tasty mineral in person, stop by the Geology Museum!

📸 Halite on Burkeite, California
📸 Halite, Poland
📸 Halite, Poland
📸 Halite cleavage fragment

09/07/2026

Today’s Mineral Monday features hematite, the iron mineral that looks completely different depending on how it forms! Hematite is an iron oxide (Fe2O3) that is a silver color when in crystal form, but becomes reddish-brown when powdered or in massive habit. It forms when iron-rich waters react with oxygen over a long period of time, usually near an ancient seafloor or lake.

Hematite is also a major component of banded iron formations (BIFs), an artifact of the oxygenation of our atmosphere over three billion years ago! When photosynthetic bacteria released oxygen into the atmosphere, it changed the environment from reducing to oxidizing, which affected the dissolved iron in the ocean. This newly oxidized iron became insoluble, and deposited as hematite!

📷 Iridescent Hematite. Isle of Elba, Italy.
📷 Crystalline Hematite. Isle of Elba, Italy.
📷 Hematite pseudomorph after Marcasite. Waunakee, Wisconsin.
📷 Specular Hematite. Upper Michigan.

08/14/2026

Our fifth and final Beach Buddy is Phareodus encastus. A species of freshwater bony fish from the Eocene, P. encastus fossils are found in the Green River Formation of Wyoming, a former lake basin famous for exceptional preservation of fossils.

The name Phareodus means “to have teeth”, and these fish certainly did. They used their rows of chompers to hunt smaller fish and insects in the mid to deep waters they inhabited. These fish used their backloaded, backward-facing fins to dart forward, either to catch prey or escape predators. With much of their habitat being mountain lakes, long term hiding was rarely an option, so rapid bursts of speed would have suited the species well.

Modern relatives of Phareodus have been recorded as using their teeth as bars, carrying eggs or hatchlings around safely in their mouths. Mass mortality specimens of juvenile Phareodus supports the hypothesis that they traveled in groups when young, though the lack of such fossils displaying adult individuals suggests they lost their schooling tendency after maturing.

If you have ever had the experience of taking a group of kids to a waterpark, you can likely relate to this fishy chaperone. So swing on down to the museum and see the fossil in person, before heading to the waterslides.

📷 Phareodus fossil. Wyoming.

07/24/2026

Summer time is the best time for featuring some "Beach Buddies" from our exhibits and today we've got our eyes on Cupulocrinus gracilis! C. gracilis was a filter feeding crinoid that lived in the warm oceans of the Ordovician period, 470 million years ago. Despite looking like plants at a first glance, crinoids are a class of marine invertebrates! They are part of the phylum Echinodermata, which also includes starfish, sea urchins, and sea cucumbers. As filter feeders, they use thin hairs on their arms to trap their diet of plankton and small bits of organic matter in a thick mucus, pulling the food towards their mouth.

Since evolving in the early Ordovician, crinoids like C. gracilis have been found along warm coasts around the world. While their ancestors’ fossils are left across Europe and America, modern crinoids live in tropical waters such as those in Oceania.

As the summer humidity ramps up and you think about not moving at all, swing by the museum and see these fossils for inspiration!

Photo 1📷 - Cupulocrinus fossil. Beaver Dam, WI. Donated by H. Hempel 1979.

07/17/2026

We're enjoying summer with some of our "Beach Buddy" specimens on display in the museum. Our third featured fossil is Inoceramus platinus, an enormous clam, commonly reaching four feet in diameter! The shell has a distinctive texture earning it the nickname “fiber shell” from the fibrous bands of calcite deposited clam grows. These crystals create a play of colors on the inside of the shell in life, and in particularly well-preserved fossils, you can still find the plate of mother-of-pearl that lined the inside.

It is hypothesised that these clams grew to their large size as a way to adapt to the murky, oxygen poor shorebeds that they inhabited. The higher surface area gave these filter feeders more opportunity to pull oxygen from the surrounding water and filter nutrients from floating silt. However, growing to such a size in these murky waters has a tendency to make you a part of the seafloor. Many specimens have been found with their shells densely covered by other smaller oysters and mollusks who used I. platinus as a substrate for their own development. Luckily, with the clams’ immense size and disinterest in moving, this colonization by other species likely didn’t harm I. platinus in any way.

As temperatures spike, and you dream of drifting in a lazy river or taking a cool mud bath, Come check out the museum, and see the species that beat the heat first.

Photo 1📷 - Inoceramus fossil. Logan county, Kansas. Collected on a museum expedition, 1991.

07/15/2026

Yesterday, our intrepid field crew set off for their annual field work. These hands-on scientists will spend the better part of two weeks in the Wyoming sun, looking for Mesozoic material to bring back to the Museum. We wish them fair fortune and a whole lot of fun!

07/10/2026

Throughout the summer we're featuring a few specimens we're calling our "Beach Buddies". Today the spotlight is on Collignoniceras hyatti, an ammonite that lived around 90 million years ago, during the Late Cretaceous. Fossils of C. hyatti are found in western North America, revealing that this animal lived in the Western Interior Seaway present during the time. Their shells are distinguished from other ammonites by the prominent spines, or “tubercules”. Like all ammonites, C. hyatti continued growing its shell throughout its life, building larger and larger segments as its body grew. Only the largest last segment, or body chamber, held the animal, with the leftover interior rooms being filled with air and water, providing buoyancy in the water.

Despite the similarities in their shell shape, ammonites are more closely related to squid, octopi, and cuttlefish than to snails or nautiloids. Recent discoveries and advances in analysis are adding to our limited knowledge of the soft parts of these interesting and beautiful creatures.

Photo 1📷 - Collignoniceras hyatti fossil. Donated by Mr. and Mrs. Emory Pittenger, 1985
Photo 2📷- Collignoniceras drafting. Figure originally produced for description in “C. woollgari, England”.

07/08/2026

As the quarterfinals of the World Cup come around, it's time for Part 3/4 of World Cup Wednesday, where we show off our best specimens from World Cup nations!

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🇲🇦: Dicranurus. Morocco. On display.
🇳🇿: Ferruginous Opal. Near Waihi, New Zealand. In collection.
🇳🇴: Zoisite var. Thulite. Norway. In collection.
🇵🇦: Fossiliferous limestone. Garachiné, Panama. In collection.
🇵🇾: Trilobites, brachiopods, and tentaculites. Paraguay. In collection.
🇵🇹: Apatite. Panesqueira, Portugal. In collection.
🏳: Diplacanthus triatus. Old Red Sandstone, Camric, Scotland.
🇿🇦: Thrinaxodon. Karoo Supergroup, South Africa. On display.
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07/06/2026

Our Mineral Monday subject is a mineral so soft, you can scratch it with your fingernail! Gypsum is an evaporite mineral, meaning it forms when shallow seas or other saturated waters evaporate, leaving behind minerals layer by layer.
Gypsum comes in many different shapes and sizes! Some gypsum forms as selenite, clear crystals that can grow to the size of a fridge (or even more - check out pictures of the Cave of the Crystals in Mexico!). Satin spar, on the other hand, forms as long, thin bundles of fibers that shimmer like silk. There are many shapes that this versatile mineral can take. Once out of the ground, gypsum shows up in places you wouldn’t expect: drywall, plaster, and classroom chalk are all some of the many uses for the soft evaporite!
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📷 Fishtail selenite. Mexico. Donated by R. Botts, C. Pluth, and Madison Mineral and Lapidary Club, 1979.
📷 Desert rose gypsum. Locality not recorded.
📷 Gypsum. South Australia.

07/03/2026

With the weather heating up, the sand and shores are calling our name. The Geology Museum is getting in that summer mood by sharing “Beach Buddies”, a collection of our specimens that made the most of the warm weather and inland seas of the past.

Our first Beach Buddy is Hesperornis, a flightless diving bird that swam the coasts of America’s Western Interior Seaway during the Late Cretaceous period, about 70 million years ago. With wings as useful as wisdom teeth, Hesperornis was shaped more like a bowling pin than a modern bird. This made them swift and agile under the water, but awkward and slow on land. Unable to place their feet fully under themselves, they likely moved over sandy beaches by sliding on their bellies, similar to loons of today.

Hesperoronis’ jaws also serve as evidence for the connection between birds and dinosaurs. They had dual-natured jaws, with the front half encased in a keratin beak, and the back half lined with a single row of teeth optimized for catching fish. This structure is a link in the evolutionary chain of beak development from more reptilian jaws

As the summer starts to appear and you long for cool water, swing by the museum and draw inspiration from our own swimming extraordinaire.

Photo 1📷 - Hesperornis fossil composite skeleton. Composite elements by Patrick Druckenmiller
Photo 2📷 - Hesperornis chick and parent. Painting by Eleanor Kish.

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http://www.geologymuseum.org/, https://news.wisc.edu/visiting-journalist-gets-close-up-look-at-geology-museums-treasures

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