Muriatic acid (aka Hydrochloric acid) is a strong acid that is frequently used in homes and businesses. You can use it to process leather, pickle steel, change pH, and clean off rocks.
In this article, you’ll learn the 3 things you need to know about the acid before you start using muriatic acid to clean your rocks.
What to Use Muriatic Acid For (in Rockhounding)
In general, we see it used to remove carbonates like calcite that obscure other mineral crystals, and to remove iron oxide rust stains.
You can’t use it for everything, so know what you have and confirm in advance that it is okay to use the acid on your piece.
Pyrite is an example of a specimen that you shouldn’t use this acid on. Calcite is another, unless you want the calcite to dissolve.
Cleaning Rocks with Muriatic Acid (How-to Step-by-Step)
- Read the details below about the dangers of muriatic acid.
- Set up your workspace. We like having a few containers that can handle the acid, as well as a bucket of water so we can pull pieces out and clean them off quickly.
- Wash the pieces you want to clean up in advance, and give them time to dry out completely.
- Decide what sort of concentration of the acid you will need.
- Put your rocks in the vessel (glass or acid resistant).
- If you are going to dilute your acid, first pour the water into your vessel (glass or acid resistant). Then add the acid you need.
- Watch the pieces carefully, but it can take anywhere from a few minutes to many days to achieve your goals. When the pieces appear to look the way you want them to look, remove them from the solution and clean them thoroughly.
- Neutralize the acid before you get rid of it.
If you aren’t sure what you are doing or whether the acid will work well on the piece you are cleaning up, it is a good idea to try the method on a similar piece that is less valuable to you.
Please note that if your specimen contains calcite, the solution will foam/bubble up. Make sure not to let any of the solution get into your eyes, or onto your face/skin.
People disagree about whether to dilute the acid or use it straight. I tend to be conservative, and look to use a more diluted solution.
This allows me the opportunity to watch the piece and remove it before the acid does more work than I want it to. But others prefer to use it straight and get good results.
3 Things You Should Know Before You Use Muriatic Acid
Muriatic Acid is Highly Corrosive and Reactive
Muriatic acid is strong, which is why people like to use it. That being said, because it is so strong, we need to take extra precautions while using it to avoid getting hurt using it.
Exposure to the acid can damage skin, eyes, and lungs irreversibly.
If you are going to use it, always wear protective gloves, close toed shoes, long pants, and long sleeves. Wear goggles. Work in a well-ventilated space or outside, or use a respirator. Keep it off your skin and any surface you care about.
When you are finished with it your mixture of the acid, neutralize it with baking soda before pouring it into the sink or onto the ground.
Not All Muriatic Acid on the Store Shelf Is the Same
There is no standard concentration of muriatic acid. This means that when you grab a bottle of it off the shelf at your local grocery or hardware store, it might be 31.5% or 14.5%.
Keep an eye on your labels and plan ahead of your trip to the store for what concentration you need for your project.
For example, this bottle of Muriatic Acid Concrete Cleaner has a concentration of 32%, but would definitely get the job done.
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Mixing Muriatic Acid With Other Cleaning Agents is Dangerous
If you are going to use muriatic acid, we definitely don’t recommend that you purposefully or even accidentally mix it with other cleaning products.
You may unknowingly cause a chemical reaction that could produce something very harmful (like toxic gas).
We see people doing it in their homes when mixing vinegar and bleach. Let’s say you are cleaning your toilet with vinegar and baking soda to try and have less impact on the environment.
The waterline ring doesn’t come off despite tons of scrubbing with the baking soda. You reach under the sink for your powdered Ajax (with bleach). You dust it into the toilet bowl and go to town with the scrub brush.
Result? Toxic chlorine gas.
Let’s look at how this could play out when you are trying to clean up some rocks/minerals/gems. You try cleaning the rocks with a brush, you try soaking them, you try soaking them in vinegar.
When you don’t get the results you want to see, you decide to drop a quick splash of muriatic acid into the concoction you’ve made.
In general, we don’t recommend that you mix muriatic acid with any other chemical or cleaner, unless you know what you are doing.
Muriatic is a decently effective, but because of the dangerousness of the chemical, is not generally where we start.
You may be able to get decent results with water and a toothbrush, or using gentle dishsoap, or with soaking in vinegar.
However, how you proceed with cleaning a specimen depends on what the specimen is. Some substances should not be immersed in water, for example, such as malachite.
As such, we always recommend that you have a plan for the specific rocks/minerals/gems that you are handling, before you just dump the entire results into a bucket and run water all over it.
If you want to know more, check out our Yes Dirt Knowledge Vault, where you can find all kinds of articles for folks who are passionate about rocks and the outdoors.