What Is a Geode? Geodes are spherical to subspherical igneous structures with a mineral-lined interior cavity. Their outer wall is more resistant to weathering than the surrounding bedrock. This enables the geode to remain intact as the surrounding bedrock erodes.
The mineral lining the cavity is typically an iridescent druse of tiny quartz crystals overlaid by numerous bands of translucent grey and white agate. Numerous are lined with more extraordinary treasures.
Other common linings include rich purple amethyst, perfect white calcite crystals, and colourful banded agate. Rare geodes can be filled with stunning blue gem silica, pink rhodochrosite, spectacular opal with vivid colour play, or other rare substances. Geodes range in length from less than one centimetre to several metres. Most geodes appear to be ordinary rocks from the outside, but their interiors can be breathtaking.
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Numerous methods exist for cleaning geodes. You must be careful not to destroy microscopic crystals when utilising these methods. Use appropriate safety precautions when cleaning geodes with chemicals.
Inspect the interior of the geode visually for microscopic minerals, such as goethite, millerite, and kaolinite, prior to performing any operation. These are extremely minute and easy to miss. Scrubbing and/or chemicals will damage some tiny crystal inclusions.
Smythite, siderite, goethite, millerite, and strontianite are a few difficult-to-find crystals that are typically lost when a rockhound cleans a specimen with a brush and water. If the geode has an iron oxide stain (brown mud colour) when it is opened, it is highly likely that these crystals have been destroyed.
EASY METHOD: Simply wash the geodes in plain water with a bit of laundry detergent (or dish soap), and then let them soak in a tub containing 1/4 cup of common household bleach for two days. This removes the majority of the coarse dirt from geodes. Lastly, clean the geode with a standard or electric toothbrush and ordinary denture cleaner, covering all crevices with the denture cleaner and brushing until all grit is removed and the crystals are clean and brilliant.
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WOOD BLEACH (OXALIC ACID) This method is preferred if your geode is stained with iron. Remove all mud and grime from the geode with a high-pressure spray. Make an oxalic acid solution, 1/8 cup oxalic acid per 5 litres of water is suggested. Soak the geode in wood bleach; for the first few hours, soak the geode for only a few hours to avoid damaging it. If the geode is still stained following the initial soak, soak it for longer or increase the concentration. Wash the geode thoroughly with warm water once the soaking process is complete. To neutralise the solution, add baking soda to wood bleach prior to disposal.
Caution: bleach for wood can harm calcite crystals and carbonates. If you know or suspect you have either of these, you can apply a diluted wood bleach solution to the geode with a paintbrush and then immediately soak it in warm water after it has been cleaned.
WARNING: Wood bleach is a carcinogen! Avoid injury by donning eye protection, gloves, and a respirator mask approved by NIOSH. Do not store wood bleach in metal containers because it is corrosive and will eat through the metal.