Cleaning Rock and Mineral Specimens
First inspect the inside of the geode looking for
microscopic minerals like goethite, millerite, or kaolinite
that are very tiny and easy to overlook. Small crystal
inclusions will be damaged by these cleaning processes. Scarce
crystals like goethite, Smythite, siderite, millerite, and
strontianite are often destroyed when cleaning the specimen
with a brush and water. If the interior of the geode has
iron oxide stain, a brown mud coloring the interior, these
crystals most likely have already been destroyed. Whichever
method you use be careful in the cleaning process, follow
the instructions for all chemicals, and wear proper
- EASY METHOD
Wash the geodes in plain water with a bit of laundry detergent or
dish soap. Then soak them, completely covered, in a tub of water with
1/4 cup of ordinary household bleach for two days. This removes most
of the heavy grit. Next use a toothbrush
and ordinary denture cleaner to brush away the remaining grit.
Make sure to cover all the crevices with the denture cleaner and
carefully brush until all the grit is removed and the crystals are
clean and bright. Wash with warm water to remove any remaining
bleach solution and allow to dry.
- OXALIC ACID METHOD
This method is more effective if there is iron staining in your
geode. Be aware that oxalic acid can harm calcite crystals and
carbonates. Oxalic acid (also called wood bleach) is toxic. Make
sure to wear proper eye protection, gloves, and a NIOSH-approved
respirator mask and follow all safety precautions and instructions
on the oxalic acid. Do not use this method in metal containers as it
is corrosive and will eat through metal containers.
precautions to take when working with any acids include:
- Only use clearly labeled chemicals and store them in a
secure area away from pets and children.
- Keep a large container of clear water handy to wash off any
- ALWAYS wear safety goggles & rubber gloves.
- Never pour water into acid - always add acid to
- Don't work alone.
- Work carefully to avoid splattering. Protect your work area.
- Keep an ample supply of baking soda handy for acid spills.
- Keep an ample supply of vinegar for alkali spills.
- Rinse specimens well.
- Dispose of all left over solutions properly.
Your Oxalic Acid Solution:
- Purchase a one pound box of oxalic
- Fill a plastic one gallon container
3/4 full with distilled water.
- Pour in the oxalic acid crystals
being careful not to inhale the powder.
- Stir for five minutes until the
crystals are dissolved.
- Add distilled water to create a full
Your oxalic acid
solution can be reused many times. When it turns a deep
green, it is time for a new batch. Neutralize the old
solution by adding baking soda until the mixture no
longer bubbles and then dispose properly.
Rinse the geodes using a high pressure spray, removing all mud and
dirt. Place your specimens in a plastic container and add enough of
the oxalic acid solution to cover them and soak. The
amount of time depends on the degree of staining. You
may only need to soak them for a few hours or up to
several days. When they are clean, remove them from the
oxalic bath and wash thoroughly with warm water. If you
have hard water in your area, it is smart to use
distilled water for rinsing. For geodes containing calcite or carbonate
crystals, you can brush on some diluted solution and as soon as it is
clean wash and soak with warm water.
Quartz crystals and
formations can be stained red-brown from iron, crusted with
clay or coated in tougher minerals like limonite or calcium.
With some work and the right techniques and cleaners you can
reveal the sparkling beauty of your find.
- INITIAL CLEANING
you need to remove any clay covering your specimens. For a prize
specimen use old toothbrushes, toothpicks, and bamboo skewers. If you have intricate formations or a lot of specimens, try
putting them outside in the shade to dry to the point where the clay
cracks, then hose with spray nozzle set at maximum force. You will
likely need to repeat the process several times, allowing the clay
to completely dry between hosing. Make sure you do not do this in a
sink or bathtub as clay will clog the pipes - do it outside! Make
sure all clay is removed before moving on to your next step.
- REMOVING ALGAE
If your specimen has organic material like algae on it, use
household bleach to clean it. Rinse well and let it dry for a good
day before using any acid cleaning method.
- REMOVING IRON STAINS
Put the specimens in a plastic bucket and cover them with our
prepared oxalic acid solution as outlined above.
Be aware that too much time in the solution can turn quartz yellow. Let your
specimens soak for one to several days.
If staining is very heavy or you want to speed the process along you
can heat the solution by standing the bucket in the hot sun. There
are some who use an old crock pot instead of a plastic bucket, and
heat their acid solution that way. If you choose these methods
- DON'T heat the solution
on your kitchen stove and never boil the solution - it puts off
- DON'T use any kind of
- DO this procedure
- DO wear rubber gloves at
When the crystals are clean to your satisfaction, rinse and rinse and
rinse them. If you have hard water in your area, it is smart to use
distilled water for rinsing to prevent possible yellow staining.
Soak them in clean water for a day and then allow to dry. If the
crystals develop a powdery coating as they dry, soak them in a
baking soda solution of about 1/3 cup to a gallon of water then
rinse them well.
methods for removing iron stains include:
- Iron-out: A commercial bisulfate cleaner used for
getting iron stains out of kitchen and bathroom fixtures.
Follow all precautions outlined by the manufacturer. Add
about 1 tablespoon of Iron Out to a pint of warm water in a
plastic bucket or container. Soak your crystal clusters in
the Iron Out solution for 5-20 minutes or up to a maximum of
1-2 hours and then thoroughly rinse your mineral specimens.
The liquid can be poured down the drain
- Naval Jelly: Contains phosphoric acid and is sold
for getting rust off metal but will work on quartz crystals.
Follow all precautions outlined by the manufacturer. Just
paint it on and then wash it off.
- REMOVING LIME CARBONATES, CALCITE, AND
First try cleaning them using ordinary White household
vinegar and washing ammonia. Soak your specimens for 8-12 hours in
full-strength vinegar. Wash the crystals well and then soak them for
an equal amount of time in washing ammonia. Rinse well and wipe dry.
If they are not completely clean, repeat the process. You may need
to repeat several times.
Very resistant calcite encrustations, limonite or other tough
mineral coatings on quartz may require you to wash them in a
muriatic (dilute hydrochloric) acid solution.
WARNING: If the specimen contains pyrite crystals
muriatic acid will damage the pyrite. Also remember that calcite
crystals should never be treated by this process. Muriatic acid
(sold as concrete or pool cleaner) is much stronger than simple
vinegar or oxalic acid, and must be used with extreme caution.
You'll need rubber gloves, goggles, large boxes of baking soda, 5
plastic buckets, and a secure outdoor space to work in:
- In the first DRY bucket put your DRY crystal specimens that
- Fill a second bucket with water for rinsing
- Your third and fourth bucket are filled with a strong baking
soda solution to neutralize the acid.
- The fifth is for draining the muriatic solution into when
you need to check the progress of the cleaning.
You can use the muriatic full strength or dilute it. If you DO
dilute it remember to add the acid to the
water. Wearing gloves and goggles, pour enough muriatic
acid over the crystals to completely cover them. Be careful not to
breathe the fumes from the acid! Expect the solution to bubble
vigorously if you are removing calcite or other alkaline minerals. In most cases you can leave the solution to work until
this action stops. Check your quartz clusters after
five minutes as sometimes they are held together by
calcite and you will end up with a bunch of loose crystals.
When they are clean to your satisfaction you need to neutralize
the acid. Remove them to the baking soda solution for 15 minutes,
then proceed with rinsing. Because the acid has penetrated the
specimen it is best to wash very thoroughly. A good rule of thumb is
total washing time should be three times the duration the specimen
was in acid. If you just briefly dipped it for 5 minutes to remove
some calcite then a 15 minute wash will be adequate. If you left your quartz specimens in for for a full day, then you should rinse
them for at least three days. Washing is basically placing your
specimens in clean water and keeping the water clean as the acid
diffuses out of the specimens. It is best if you can set a water
supply on a slow trickle into the bucket to constantly provide clean
water. Otherwise changing the water as often as possible will work.