These beautiful aragonite crystals are grown straight from a rocks, with just a little help from vinegar.
We do so many cool projects that never make it onto TinkerLab. I wish you could see the stacks and stacks of photo files that are just waiting to be shared here. I am seriously in need of an assistant (who’s over six years old)!
A little over two years ago we grew a batch of amazing aragonite crystals. Have you heard of these? They are incredible: easy to grow, not expensive, and they offer up a cool lesson in geology and chemistry.
After digging around in our science cabinet the other day, I found the old box of dolomite rocks, which are the base for these aragonite crystals. And there were still about 20 rocks in there, just waiting to grow crystals on them!
Without further ado, I’d like to introduce you to aragonite crystals…
Ingredients for Aragonite Crystals
You will only need two ingredients for this project:
Distilled White Vinegar
Simple, right? (Honestly, I love simple)
Where Can I find Dolomite Rocks?
I found the BEST source for these rocks at Educational Innovations. They’re priced fairly – you can buy 25 rock samples for just $8.95, which is AWESOME if you’re a classroom teacher or interested in gifting these to a bunch of friends as we have. I’m not affiliated with this company, just a happy customer. I’ve done a thorough search and there aren’t a lot of places to find these (easily).
How to make Aragonite Crystals
I poured the rocks into a bowl and invited each child to pick their favorite one. Flat, tall, fat – sooo many choices!
Once the rock was selected, we placed it in a small glass mason jar. We used 4 oz. mason jars by Bell (affiliate), and I find ALL sorts of uses for these in our art and science projects. We store homemade paint in them, turn them into artistic tea light holders, and use their larger cousins for our new solar lights.
You can put it in any glass or ceramic container. Because I’m hugely in favor of putting kids to work (i.e. empowering them), I then poured the vinegar into a small pitcher and invited the kids to p0ur the vinegar into the jar.
The trick is to pour just enough vinegar into the jar so as not to cover up the top of the rock. Do you see that dry spot in the bottom right picture?
After five days, our crystals looked like this:
About half of the vinegar had evaporated, some crystals formed along the edges of the jar, and a small mound of crystals were growing on top of our rock.
The crystals are fully formed after about two weeks, once all of the vinegar evaporates. To speed up evaporation, place the jar in a sunny window.
What is aragonite?
The rocks we used for this crystal-growing experience are magnesium-rich dolomite. Dolomite is an evaporative sedimentary rock that’s made up of sediments and minerals. This unique variety of dolomite, found in an ancient lagoon that was surrounded by a coral reef millions of years ago, will grow white aragonite crystals when it’s placed in distilled white vinegar.
Aragonite is carbonate mineral that usually forms in oceans and warm, wet environments such as caves and hot springs. will turn into calcite over time. You can read up on aragonite here.
How to Grow Aragonite Crystals
Place your rock in a jar. You can wash the sediment off of it first, or place it in the jar as it is.
Pour distilled white vinegar over the rock until the top of the rock barely pokes above the surface of the vinegar.
Place the jar on a shelf where it will be undisturbed but easily observed, preferably a warm, sunny spot that will encourage evaporation.
Small crystals will begin to appear within a day or so.
Observe the dolomite daily to track the progress of your crystals.
Leave the jar undisturbed until ALL the vinegar evaporates and the rock is COMPLETELY DRY, which could take one to two weeks. If you move the jar before this point, the crystals may fall apart. If that happens, just place it back on the shelf and begin again.
Once dry, the dolomite and crystals can be picked up and examined. They will be hard, but a bit fragile.
More Uses for Vinegar
Vinegar and Baking Soda Experiment
How to Make Curds and Whey: A Science Demonstration
Make Natural Dyes for Painting Eggs
Try the Naked Egg Experiment (free activity from the TinkerLab book – affiliate)
For more ideas that circle around the theme: GROW, I’m joining a creative group of engineers, scientists, educators, and artists to share projects that circle around STEAM (science, technology, engineering, art, and math) ideas. This week’s theme is GROW, and you can see the other grow-related ideas here:
DIY Crystal Landscapes | Babble Dabble Do
10 Ways to Use Tinker Trays | Meri Cherry
Transforming Ninja Stars | What Do We Do All Day?
14 Activities with Balloons | All For The Boys
Biology of Yogurt | Left Brain Craft Brain
STEAM on Pinterest
You might also enjoy following my STEAM + STEM Activities board on Pinterest for more ideas like this.
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[…] How to Grow Aragonite Crystals // TinkerLab […]
The crystals are gorgeous! And I loved learning about aragonite. This was a new one for me.
Thanks so much, Anne. I did a pretty extensive hunt for info on aragonite and it’s not widely discussed. Maybe this will help it become one of the popular kids in the crystal world!
This is so cool!
I have never herd of aragonite crystals! These are incredible! Off to order some dolomite rocks STAT!
[…] How To Grow Aragonite Crystals – Tinkerlab […]
[…] How to Grow Aragonite Crystals // TinkerLab […]
Hello! Thank you for such an awesome science experiment. I’d like to try this with my two kids. I was wondering if adding color would ruin the experiment or if it was not recommended. Thanks so much!
Sorry, but you did not precipitate aragonite. You precipitated calcium acetate.
I was thinking the same thing. I’ve done a fair amount of experiments with vinegar. Try putting the vinegar in the jar without the rock. Similar crystals will form on the sides of the jar as the vinegar evaporates, because what’s evaporating is mostly water, and the acetic acid (distilled white vinegar is around 4% acetic acid and 96% water) is crystallizing.
Putting the vinegar in with a rock or anything else might allow the acetic acid to form compounds (like calcium acetate) that can also produce (different) crystals. Acetic acid is a compound of carbon, hydrogen, and oxygen. Aragonite is a compound of calcium, carbon, and oxygen. If aragonite was being produced by a reaction of the acetic acid with calcium in the dolomite, a lot of hydrogen would be being released. Those jars show no signs of bubbles or any other evidence of hydrogen precipitating out of the fluid, so there is no way this can be producing aragonite.
I agree with Mike, those are probably calcium acetate crystals (as they look slightly different from the pure acetic acid crystals I have produced). The acetic acid probably is reacting with calcium in the dolomite, but it isn’t releasing the hydrogen atoms, so it isn’t becoming aragonite.
On a side note, you should be able to do something similar with any kind of porous stone. If there is no calcium to react with, you will just get straight acetic acid crystals which are quite pretty in their own right.
On a side side note: Try putting some copper wire in vinegar. Note that the solution created will contain toxic copper acetate, so it may not be suitable for young students to work with, without close supervision. The solution will turn a very vivid blue. If you put a lid on it, so the water won’t all evaporate, this can precipitate out extremely dark blue (almost black) crystals, which can be ground to powder and used as pigment. This is a slower process than evaporating vinegar to make acetate or calcium acetate crystals, and if the vinegar is allowed to evaporate, you will end up with mostly white acetate crystals, not dark blue copper acetate. (It might also help to periodically pour out the vinegar and add fresh vinegar, though I haven’t tried this yet…)
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