Cleaning Rock and Mineral Specimens

GEODES
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 protection.

• 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.
  General precautions to take when working with any acids include:
  1. Only use clearly labeled chemicals and store them in a secure area away from pets and children.
  2. Keep a large container of clear water handy to wash off any chemical spills.
  3. ALWAYS wear safety goggles & rubber gloves.
  4. Never pour water into acid - always add acid to water.
  5. Don't work alone.
  6. Work carefully to avoid splattering. Protect your work area.
  7. Keep an ample supply of baking soda handy for acid spills.
  8. Keep an ample supply of vinegar for alkali spills.
  9. Rinse specimens well.
  10. Dispose of all left over solutions properly.

   

  To Prepare Your Oxalic Acid Solution: Purchase a one pound box of oxalic acid. 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 gallon.

  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
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
  First 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
  1. DON'T heat the solution on your kitchen stove and never boil the solution - it puts off poisonous fumes.
  2. DON'T use any kind of metal container
  3. DO this procedure outside
  4. DO wear rubber gloves at all times.

  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.

  Other methods for removing iron stains include:

  1. 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
  2. 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 BARITE
  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 need cleaning.
• 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.

OTHER RESOURCES:

• Utah Geological Survey
• John Betts Mineral Cleaning Article
• Field Collecting for Gemstones and Minerals by John Sinkankas
• Gemstone and Mineral Data Book