How to Clean Crystals and Mineral Specimens Without Damaging Them

Start with the gentlest method

Work up from dry to wet to chemical, and stop as soon as the piece is clean. Most damage comes from using a stronger method than the specimen needed.

• 1. Dry: a rubber air blower or a soft paintbrush removes most dust and loose grit. This is safe for every mineral.
• 2. Water: a quick rinse in lukewarm water, with a drop of mild soap and a soft toothbrush for dirt. Only for minerals that do not dissolve or hydrate, and dried straight away.
• 3. Soaking or chemicals: only for robust minerals, only when you know what the mineral is, and never on a piece you cannot identify.

Three ways cleaning destroys specimens

Almost every cleaning accident falls into one of these:

• Water-sensitive minerals: gypsum, and therefore desert roses, dissolves slowly in water. Erythrite holds eight water molecules in its structure and should never be washed. Cobalt arsenides such as skutterudite tarnish faster when damp.
• Acid-sensitive minerals: carbonates fizz and dissolve in acid, even in vinegar or lemon juice. That includes calcite, aragonite, azurite, malachite and cerussite. Acid also removes the lustre from anything it does not dissolve completely.
• Heat and vibration: heat destroys azurite and changes the colour of amethyst. Sudden temperature changes crack cerussite and fluorite. Ultrasonic cleaners shake apart cleavable or hydrated minerals and loosen old repairs.

Iron stains and oxalic acid

Rusty-brown iron stains on quartz are commonly removed with oxalic acid, which works because it forms a water-soluble complex with ferric iron. It is the active ingredient in some household rust removers.

It is still an acid. Keep it away from carbonate minerals, which it attacks, and from anything you have not identified. Oxalic acid is toxic if swallowed and concentrated forms cause chemical burns: use gloves and eye protection, work outdoors or ventilated, and rinse the specimen thoroughly afterwards. For a valuable piece, ask the seller or a club before trying.

Crystals that can't go in water, salt or the sun

These three questions come up more than any other, and the answers are physical, not spiritual:

• Not in water: halite (rock salt) dissolves outright; gypsum, selenite and desert roses dissolve slowly and are scratched by a fingernail; erythrite and other hydrated minerals are damaged by washing; skutterudite and other metallic arsenides tarnish faster when damp.
• Not in salt or salt water: salt crystallises inside cracks and pores as the piece dries and can split it from inside. Avoid it for anything porous, cracked or soft, and never use it on soluble minerals.
• Not in strong sun: amethyst's colour comes from colour centres that light can alter, and some specimens fade; kunzite is known to fade in sunlight; some coloured fluorite fades too. Display these out of direct sun.
• Moonlight, smoke and sound do no physical harm to any mineral.

Cleaning crystals you found or dug yourself

Field-collected specimens are usually coated in clay, iron oxide or calcite crust.

• Soak in plain water to soften clay, then brush with a soft toothbrush. Repeat rather than scrub hard.
• A wooden toothpick lifts dirt from between crystals without scratching.
• Iron staining on quartz: oxalic acid as described above, never on carbonates.
• Identify the mineral before using anything stronger than water. If you cannot identify it, stop at water.

Care table for Moroccan minerals

What each mineral tolerates, from the guides on this site. When in doubt, dust only.

• Desert rose
• Erythrite
• Calcite
• Malachite
• Amethyst

After cleaning

Dry the piece completely before putting it away, on a towel and out of the sun. Store each specimen so that nothing touches its crystals: a padded box, a small stand, or a case. For lead, copper and arsenic minerals, wash your hands after handling and keep them away from children, pets and food.

Questions collectors ask