What is Pictured? Hoarfrost or Rime Ice?

While winter may cause people in the north to endure exceptionally tough conditions at times, this season also provides an untouchable beauty. After a night of temperatures that reached below 0F, I quickly fed some frosty animals on my farm and tried to ignore the biting sting in my fingers; then, I stopped in awe! I hadn’t noticed the astonishing wonderland that surrounded me. Throughout the night, crystals had formed all over the farm. The trees were caked in sparkling beauty and there were fan-shaped crystals covering sticks and objects on the ground below. As painful as my fingers were, I took out my camera and took some pictures of these crystals and the stunning white paradise.



How do these crystals form and what causes them?

I figured these crystals were some kind of frost but I had to do some research to be sure!

From what I read, the crystals pictured are either hoarfrost (a type of frost) or rime ice.



Hoarfrost (also known as radiation frost) forms when the water in the air freezes when it contacts cold objects. The water exists as a gas in the air and as it freezes it changes from a gas to a solid (also known as desublimation).

Rime ice is formed when liquid water in the air freezes upon contact with other objects. Usually this is in the form of fog and is the water changing from a liquid to a solid. The water in air needs to be warmer than 32F and usually one cannot clearly see the crystalline structure.

Now that you have a little background of the differences between hoarfrost and rime ice, I will provide the conditions surrounding the formation of the crystals pictured. Take your best guess if these are hoarfrost or rime ice!

During the day before these crystals formed, the temperature reached 35F. That night and early the next morning temperatures fell to -1F. There was hardly any wind (2 – 5 mph). No fog was observed.

Are you ready to take your best guess at which formation this is?

Drumroll please….

I believe it is….


The crystals are most likely hoarfrost. Water that was in the air as a gas cooled so quickly that it skipped condensing into a liquid and froze directly from the air (desublimation). This created the appearance that the ice crystals grew and fanned outwardly. In addition, no fog was observed and the temperature was too cold for fog to be present which means that the water that formed the crystals needed to be in a gaseous state before freezing.

This is my best guess but I would love to hear your thoughts / ideas! Please comment!

Frost2 Frost3

Endless Discoveries

Do you know what I love about science?  It is the ENDLESS discovery; the excitement of finding something really cool and learning along the way!

This summer while hiking with my daughters, we came across this pink and fuzzy THING on an oak leaf.


I had NO idea what it was!  caterpillar, no….fungus, no, ….disease, no!  I couldn’t figure it out.  We saved the mysterious object in the refrigerator and, off and on for weeks, we searched online trying to solve the mystery.

Finally, during a fly fishing demo, we spoke with a Park Ranger, and she knew just what it was!  It was an insect gall.  Insect galls are growths that develop on plants.  The plant reacts to a wound created by the insect.  Apparently, a gall wasp, Callirhytis furva, will implant an egg into a leaf of an oak tree.  After the egg turns into a larva it will cause the oak tree to grow this pink and fuzzy gall on the leaf.  The larva will then grow while it is protected by a hard, fuzzy gall covering.  Isn’t that cool?

My girls and I were incredibly excited about the search for information about this unknown object.  I must admit that the search itself was even more exciting than finding out the answer!

This is one of the most fantastic and addicting parts of science…the search for information!  I have found that, in science, as more knowledge is gained, more questions are created.  Doesn’t this picture make you want to know more about the gall wasp?  I bet you can’t wait to learn more about it!  🙂

Go for a walk with the children that you know to look for galls and rear the insects at home.  Encourage their questions as you all make discoveries!  We had many more questions after our findings:  What does a gall wasp look like?  Does it have pink and yellow on its body?  Do all oak trees make galls with that color combination? The questions are endless…and so are the answers!

We hope that you enjoy the fall and have some exciting discoveries together!  We would love to hear about your science adventures!  Please feel free to comment.


Corrine Knight


~Sharing the Love of Science~

Welcome to Jumbo Minds!

The Jumbo Minds founders love – love – love science! I graduated from college with a biology major and chemistry minor. My sister also shares the love, and has taught science and math in elementary, middle, and high school. One day, while on vacation, she and I were talking about how to share this love with our children.

I had a toddler at the time, and used to do silly things like blow on a house plant and say, “Here’s some carbon dioxide, plant!” Then I’d take a deep, exaggerated breath and say, “Oh – thaaaank you for the oxygen!!” As topics occurred to me, I’d have conversations with my kiddos about digestion, precipitation, photosynthesis, and temperature, to name a few.

My sister and I realized that, while it was easy for us to speak ‘science’ with our children, many other parents haven’t had the same exposure we’ve had. That could make science harder to discuss! We hatched a dream to write science books for children. This dream, to share science with children, parents, and teachers, has been slowly growing. Our next posts will describe some of the things we’ve learned along the way. Stay tuned!