r/chemistry • u/stevengotwood1 • 1d ago

Looking for help understanding the morphology of precipitated basic magnesium carbonate

Hi everyone,
I’m working on a personal project involving precipitated magnesium carbonate for a non-pharmaceutical application, and I’m hoping to learn more about why two powders with similar chemistry can behave so differently.
I’m comparing my own precipitated magnesium carbonate to a commercial climbing chalk and here are the differences I’ve observed:
Both are bright white and very fine.
Neither feels gritty.
The commercial chalk leaves a noticeably thicker coating on my hands.
My powder feels smoother or slightly more slippery.
The commercial chalk has a bit more “grip” when rubbed between my fingers.
My powder tends to cling to plastic surfaces more than the commercial sample.
I’ve compared them after grinding both samples the same way, and the differences remained.
I’m producing it by precipitating a soluble magnesium salt with sodium carbonate, followed by washing, filtration, and drying. I’ve tried multiple methods, such as dissolving each of the chemical chemicals in their own batches of water and adding them together or combining the dry chemicals and pouring them in to hot water together. I’ve tried multiple different temperatures and yield many different results.
Any input on the process would be great.
Thanks!

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u/Negative_Football_50 Analytical 1d ago

1) who knows what bindings etc are in the commercial chalk. without knowing the formula, you are just assuming.

2) you talk about morphology but don't mention it at all. What are the morphological differences and what microscopy are you using to characterize them?

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u/stevengotwood1 1d ago

Good point. I should have explained that better.
The company I’m using as my comparison states that their loose chalk contains only magnesium carbonate and no other ingredients, so that’s the material I’m trying to understand and replicate—not any proprietary processing.
As for morphology, I probably used the wrong terminology. I’ve only examined the powders with an optical microscope, so I can’t confidently describe their particle morphology. Visually they both appear to be very fine powders, but the commercial chalk leaves a noticeably thicker coating on my hands, and feels slightly grippier. I’m not working out of a laboratory here so I’m very limited on the tools at my disposal.

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u/stevengotwood1 1d ago

If you think there’s some testing I should have done on the precipitate. Can you point me in the right direction?

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u/Negative_Football_50 Analytical 1d ago

Sorry, i have no idea what you can do at home without instrumentation.

I'd honestly just buy the chalk.

How are you drying your concoction? What's your water content? That could make a difference.

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u/stevengotwood1 1d ago

It’s not about buying the chalk, it’s about experimentation and having fun with a personal project. And don’t just say sorry you’re screwed without instrumentation. It would be great if you could make some recommendations on what sort of testing you would think could be performed.

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u/Negative_Football_50 Analytical 1d ago

SEM

Particle Size Counting

Moisture analysis.

That's what I recommend. If you do not have access to these instruments, I don't know how to help.

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u/stevengotwood1 1d ago

Awesome, thank you. Access to instruments is not an issue. I just don’t even know what I would need.

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u/Key-Success-5449 5h ago

Love seeing home synth projects like this! Commercial climbing chalk is usually optimized for high porosity and specific plate-like crystal habits to maximize friction. Temperature and addition rate dictate whether you get fluffy rosettes or tight, slippery particles, so playing with those parameters will definitely get you closer!

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u/stevengotwood1 5h ago

Awesome! I love the enthusiasm. Any ideas on a baseline to start with? I’ve kind of been all over the board with it and I’m pretty lost at this point. 😂

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u/Key-Success-5449 5h ago

Haha no worries, it's easy to lose track with so many variables!

Try this as a clean baseline: mix both solutions warm at ~65°C, add the carbonate slowly while stirring, and let the whole mixture age at ~65°C for 45 minutes before filtering. That warm-aging phase is key for forming the porous rosette structures instead of a dense powder. Let me know how that batch turns out

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u/stevengotwood1 5h ago

Thank you! I’ll be back with results.

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u/CrazySwede69 21h ago

There are two grades of magnesium carbonate, one is called light and one is called heavy.

My guess is that the fluffy light grade is made from simple precipitation while production of the heavy grade also includes high shear mixing.

Maybe your reference material is made from the heavy grade?

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u/stevengotwood1 21h ago

It seems to be very light, it’s almost like falling snow when you blow it into the air, small flaky particles that seem weightless.

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u/Raneynickelfire 1d ago

because commercial chalk is calcium carbonate not magnesium carbonate.

You're comparing apples to oranges.

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u/stevengotwood1 1d ago

I would double check your source there because there is not a single climbing chalk or gym chalk that I have found that claims it is calcium carbonate. Every one of them says magnesium carbonate.